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CASTEP user guide

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1. 1 31 e AUTO 2 For backwards compatability the string 0 is equivalent to NONE 1 to MANUAL and 2 to AUTO If FINITE_BASIS_CORR MANUAL the user must supply a value for keyword BASIS DE DLOGE The default value of this parameter is 2 if one of the following conditions are met e task GEOMETRYOPTIMIZATION geom_method BFGS fixed_npw FALSE and the cell is not fixed or e task MOLECULARDYNAMICS fixed_npw FALSE and the cell is not fixed or e calculate_stress TRUE Otherwise the default value is 0 2 40 real kind dp basis_de_dloge The derivative of total energy with respect to the log of basis cut off energy This is only used if finite_basis_corr MANUAL The default value of this parameter is 0 0 eV 2 41 integer finite basis npoints The number of points used to estimate the derivative of total energy with respect to the log of basis cut off energy The minimum value allowed for this parameter is 2 The cut off energies at which the total energy is calculated in order to estimate the derivative will be chosen equally spaced by finite_basis_spacing with the highest energy equal to cut_off_energy The default value of this parameter is 3 Only used if finite_basis_corr AUTO 2 42 real kind dp finite_basis_spacing The energy difference between cut off energies at which total energy is evaluated in order to estimate the derivative of total energy with res
2. D Segall P J D Lindan M J Probert C J Pickard P J Hasnip S J Clark and M C Payne First principles simulation ideas illustrations and the castep code J Phys Cond Mat 14 2002 2717 2744 8 D Vanderbilt Soft self consistent pseudopotentials in a generalized eigenvalue formalism Phys Re view B 41 1990 7892 7895 49
3. Not all species need appear in the SPECIES POT block If a pseudopotential is not specified the default pseudopotential parameters will be used to generate a pseudopotential for the element specified If the initial alphabetical characters of a species label is not a standard element symbol in the periodic table the potential for the species must be specified The charge on the ion for each species will be derived from the pseudopotential corresponding to that ion BLOCK SPECIES_LCAO_STATES CCC Is CCCo Ig Ize ENDBLOCK SPECIES_LCAO_STATES The first entry on a line is the symbol or atomic number of the species This must correspond with the species symbol or atomic number of the species in the POSITIONS FRAC or POSITIONS_ABS block The second number is the number of angular momentum channels to use in the LCAO basis set for the species when performing population analysis For example to use the 2s and 2p states for C The 1s state is a core state this should be 2 By default the number of states will be the appropriate number to complete the valence shell to the next noble gas If shallow core states are excluded from a pseudopotential the value of SPECIES _LCAO_STATES for that specied should be included in the cell file to ensure a meaningful basis set is used 2 2 8 External Pressure An external pressure may be applied to the unit cell by specifying a pressure tensor 11 BLOCK EXTERNAL_PRESSURE units Bs D N R
4. ZENDBLOCK EXTERNAL_PRESSURE units specifies the units in which the pressure is defined If not present the default is GPa Entry Rgs is the xx component of the pressure Rzy the xy component etc The default is to apply no external pressure 2 3 The parameters file The parameters file is a free format containing keyword value pairs one per line Any of the characters or begins a comment and the rest of the line is ignored Keyword lines take the form keyword value and any of the chacacters space and TAB may be used to separate the keyword and value It is not necessary to input the value of all parameters used Each has a sensible default and it is usually only necessary to specify a very small number explicitly Parameters whose value is a physical quantity may be given in any of a variety of units Physical quantities may be followed by a unit separated by a space The quantity will be automat ically converted to atomic units as used internally when the file is read The units which are recognised by the code for each physical dimension are listed in Tables 4 and 5 If no units are provided in the input the assumed units will be those shown in these tables The following are equivalent ways of defining a physical quantity AgeOfUniverse 24 d0 s Age_Of_Universe 24 d0 5 AgeOfUniverse 24 d3 ms The parameters file is not only read at the beginning of a run but also periodically whenever a run is chackpointed
5. for example every few molecular dynamics iterations This facility may be used to adjust certain of the parameters during the course of a run In particular adding the single line STOP will cause the run to write a check file and halt at the next checkpoint 2 4 character len file maxpath seedname The seed used for generating filenames This is determined from the command line arguments when running the executable and is set by subroutine parameters_read 2 5 character comment A comment string which may be used to label the output By default this string will be blank 2 6 integer iprint This indicates the level of verbosity of the output from 0 the bare minimum to 3 which corresponds to full debugging output The default value of this parameter is 1 12 Unit Abbreviation Dimension Identifier Value atomic units Bohr Bohr L bohr a0 1 Metre m L m i Centimetre cm L cm meca x 107 Nanometre nm L nm meca x 107 Angstrom A L ang Meco x 10710 Electron Mass me M me 1 Unified Atomic Mass Unit amu M amu Nom x 10 3 Kilogram kg M kg ma Gram g M g x 10 3 Atomic Unit of Time aut T aut gt Bi Second S T S Laime Millisecond ms T ms arme x 1078 Microsecond mus T mus cae x 10 6 Nanosecond ns T ns forme x 10 9 Picosecond ps T ps Satme x 19 12 Femtosecond fs T fs Ce my x 10715 Elementary Charge e C e 1 Coulomb Coulomb C c 2 Hartree Ha E hartree ha 1 Millihartree mHa E mhartree 1078 Elec
6. between wavefunction dumps ELEC_RESTORE_FILE S elec_restore_file Restore the wavefunction and den sity from this file on first call to elec tronic minimisation Table 10 Parameter file keywords controlling electronic minimisation continued Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string 19 Keyword Type Corresponding Description Variable Density Mixing Parameters MIXING_SCHEME S mixing_scheme The mixing scheme to use in the density mixing procedure MIX_HISTORY_LENGTH I mix_history_length The number of charge densities to store in the density mixing history MIX_CHARGE_AMP R mix_charge_amp The mixing amplitude for the charge density MIX_CHARGE_GMAX P mix_charge_gmax The maximum wavevector for which to mix the charge density MIX_SPIN_AMP R mix_spin_amp The mixing amplitude for the spin density MIX_SPIN_GMAX P mix_spin_gmax The maximum wavevector for which to mix the spin density MIX_CUT_OFF_ENERGY P mix_cut_off_energy The cut off energy for the densities within the mixing scheme MIX_METRIC_Q P mix_metric_q The metric for the densities within the density mixing scheme Population Analysis POPN_CALCULATE L popn_calculate Perform a population analysis on the final ground state POPN_BOND_CUTOFF P popn_bond_cutoff The maximum distance between two atoms for which a bond population will be outpu
7. e HF Hartree Fock e SHF Screened Hartree Fock e EXX Exact exchange e SX Screened exchange e ZERO No exchange correlation potential e HF LDA LDA with exchange contribution replaced by Hartree Fock e SHF LDA LDA with exchange contribution replaced by screened Hartree Fock e EXX LDA LDA with exchange contribution replaced by exact exchange e SX LDA LDA with exchange contribution replaced by screeened exchange The default value of this parameter is the value of xc_functional 2 84 character geom method The method of geometry optimisation to use Possible values are BFGS BFGS minimisation DampedMD Damped molecular dynamics The default value of this parameter is BFGS 2 85 integer geom_max_iter The maximum number of geometry optimisation steps to take The default value of this parameter is 30 2 86 real geom_energy_tol The tolerance for finding convergence of the appropriate free energy per atom during a geometry optimisa tion The difference between the maximum and minimum values of the free energy over geom_convergence_win iterations must be less than this value for the convergence criteria to have been met The default value of this parameter is 2 x 1075 eV atom 2 87 real geom force _tol The tolerance for the ionic force to accept convergence during an ionic relaxation The maximum ionic force must be less than this value over geom_convergence_win iterations for the convergence cr
8. effective charge tensors as part of a phonon or efield linear response calculation The default value of this parameter is TRUE 2 128 logical born_charge_sum_rule Selects whether to explicitly correct the Born effective charge tensor to enforce the sum rule that effective charges sum to zero The default value of this parameters is FALSE 2 129 integer efield_max_cycles The maximum number of cycles in the efield linear response minimiser The default value of this parameter is 50 2 130 integer efield_max_cg steps The maximum number of conjugate gradient minimisation steps in one cycle of the efield linear response minimiser The default value of this parameters is 20 2 131 real kind dp 1 efield_energy tol The tolerance for accepting convergence of the second order energy in an efield linear response minimi sation The default value of this parameter is 1 x 1078 Bohr 2 132 integer efield_convergence win The second order energy must lie within efield _energy _tol for the last efield_convergence_win iterations for the convergence criteria to be met in the efield linear response minimiser The value of efield_convergence_win must be greater than or equal to 2 The default value of this parameter is 2 2 133 logical efield_calc_ion_permittivity This logical value determins if the ionic contribution to the permitivity is calculated during an efield run The default value of this parameter is TRUE 2 1
9. energy Only used if FINITE_BASIS_CORR AUTO FINITE_BASIS_SPACING P finite_basis_spacing The energy difference between cut off energies at which total energy is evalu ated to estimate the derivative of total energy w r t log of basis cut off en ergy Only used if FINITE_BASIS_CORR AUTO FIXED_NPW L fixed_npw Flag to indicate if the basis set should be fixed during variable cell calcula tions Table 8 Parameter file keywords controlling the basis set Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value D for a keyword that may simply be defined present or not and S for a text string BASIS_PRECISION and CUT_OFF_ENERGY may not both be defined in the same parameter file 17 Keyword Type Corresponding Description Variable Electronic Parameters NELECTRONS I nelectrons The number of electrons in the system CHARGE I The total system charge SPIN I The total z component of the electronic spin NupP I nup The number of spin up electrons NDOWN I ndown The number of spin down electrons SPIN_POLARISED L Should the system be treated as spin polarised NBANDSt I nbands The number of bands NEXTRA_BANDS I The number of extra bands above Besectrons PERC_EXTRA_BANDST R The number of extra bands as a per centage above 2eectrons ELEC_TEMP P elec_temp The electron temperature for which re sults will b
10. ics MD_ELEC_ENERGY_TOL P md_elec_energy_tol The convergence tolerance for finding the ground state energy during an MD run as an energy per atom MD_ELEC_EIGENVALUE_TOL P md_elec_eigenvalue_tol The convergence criteria for an eigenvalue when perform ing DIIS DM minimisation during an MD run MD_ELEC_CONVERGENCE_WIN I md_elec_convergence_win The number of iterations over which convergence is assessed during an elec tronic minimsation in an MD run Table 14 Parameter file keywords controlling molecular dynamics continued Argument types are rep resented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string 23 Keyword Type Corresponding Variable Description Optics OPTICS_NEXTRA_BANDS OPTICS_PERC_EXTRA_BANDS OPTICS_NBANDS OPTICS_XC_FUNCTIONAL optics_nbands optics_xc_functional The number of extra bands above the number of valence bands at each k point when calculating an optical spec trum The precentage of extra bands above the number of valence bands at each k point when calculating an optical spectrum The number of bands at each k point when calculat ing an optical spectrum The functional to use for cal culating optical spectra Transition State Search TSSEARCH_METHOD TSSEARCH_LSTQST_PROTOCOL TSSEARCH_QST_MAX_ITER TSSEARCH_CG_MAX_ITER TSSEARCH_FORCE_TOL TSSEARCH_DISP
11. in this manner the absolute orientation is arbitrary In this case the orientation is defined by applying the following constraints e a lies along the x axis e b lies in the xy plane e c forms a right handed set with a and b units specifies the units in which the lattice vector magnitudes are defined If not present the default is A Angles should be specified in degrees 2 2 2 Tonic Positions The ionic positions may be specified in fractional coordinates relative to the lattice vectors of the unit cell or in absolute coordinates Only one of POSITIONS FRAC and POSITIONS_ABS may occur in a cell definition file BLOCK POSITIONS_FRAC CCC L Rii Ri Rix MAGMOM mm CCCol I2 Roi Ro Rok MAGMOM mmy ENDBLOCK END POSITIONS_FRAC The first entry on a line is the symbol or atomic number of the ionic species The correct symbol will be looked up for the atomic species if the atomic number is specified A symbol can have a maximum of three characters The first alphabetical characters identify the element from which default values for atomic mass etc The next three entries on a line in POSITIONS FRAC are real numbers representing the position of the ion in fractions of the unit cell lattice vectors If the optional flag MAGMOM7 is present on a line this sets the spin polarisation nN of the atom for initialisation of the spin density If this flag is not present a non spin polarised state will be assumed BLOCK POSITI
12. may be present in a cell file t Only one of KPOINTS_LIST KPOINTS_MP_GRID and KPOINTS_MP_SPACING may be present in a cell file Keyword Type Default Description BS_KPOINT_PATH BS_KPOINT_PATH SPACING BS_KPOINT_LIST OPTICS_KPOINT_LISTY OPTICS_KPOINT_MP_GRID t OPTICS_KPOINT_MP SPACING OPTICS_KPOINT_MP_OFFSET PHONON_KPOINT_PATHo PHONON_KPOINT_PATH SPACING PHONON_KPOINT_LISTo PHONON_GAMMA _ DIRECTIONS 0 1 Aw SCF k points 0 1 Aw 0 0 0 0 1 Aw SCF k points See text A list of k points in the Brillouin zone which defines the path along which a band structure calculation will be per formed Specifies the maximum spacing between k points along the path for which a band structure calculation will be per formed A list of k points at which a band structure calculation will be performed A list of k points in the Brillouin zone with associated weights for optical ma trix element calculations The k points for optical matrix element calculations defined as a Monkhorst Pack grid by specifying the grid dimen sions in each direction The k points for optical matrix element calculations as a Monkhorst Pack grid by specifying the maximum distance between k points The offset of the origin of the Monkhorst Pack grid for optical matrix element calculations in fractional coor dinates relative to the reciprocal lattice vectors A list of k points in the Brillouin zo
13. of the LCAO basis set used for population anslsyis may be specified in the cell definition file BLOCK SPECIES_MASS units CCC Ri CCC a Ig R ENDBLOCK SPECIES_MASS units specifies the units in which the masses are defined If not present the default is atomic mass units The first entry on a line is the symbol or atomic number of the species This must correspond with the species symbol or atomic number of the species in the POSITIONS FRAC or POSITIONS_ABS block The second entry on each line is the mass of that species Not all species need appear in the SPECIES_MASS block any not present will assume the default mass for that species If the initial alphabetical symbol specified for a species is not a standard element symbol in the periodic table the mass of the species must be specified BLOCK SPECIES_POT CCC h lt filename gt CCC o Ig_ lt filename gt ENDBLOCK SPECIES_POT The first entry on a line is the symbol or atomic number of the species This must correspond with the species symbol or atomic number of the species in the POSITIONS FRAC or POSITIONS_ABS block The second entry on each line is the filename of the file containing the definition of the pseudopotential representing the ionic species The file to which this refers may be a definition of the parameters of the pseudopotential which is to be generated at runtime or an old style pseudopotential definition containing the data for the pseudopotential
14. parameters Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value D for a keyword that may simply be defined present or not and S for a text string The keywords NUM_BACKUP_ITER and BACKUP_INTERVAL may not be defined in the same parameter file 15 Keyword Type Corresponding Description Variable General Parameters Continued PAGE_WVFNS I page_wvfns Controls the paging of large wavefunctions to disc in order to save memory RAND_SEED I rand_seed Controls the initialisation of the random number sequence DATA_DISTRIBUTION S data_distribution Controls the parallelisation strategy used by the code OPT_STRATEGY S opt_strategy Controls the optimisation strat egy used by the code OPT_STRATEGY_BIAS I opt_strategy_bias Expert control for the optimisa tion strategy used by the code DEVEL_CODE S devel_code A code for developers use to con trol specific debugging output Exchange Correlation Parameters XC_FUNCTIONAL S xc_functional The functional to use for the exchange correlation potential See Section 2 32 for details XC_VXC_DERIV_EPSILON R xc_vxc_deriv_epsilon The fraction used to determine the size of the increment used in the numerical calculation of the second derivatives of the GGA functions Pseudopotentials PSPOT_NONLOCAL_TYPE S pspot_nonlocal_type This defines the representation real or reciprocal space used for application
15. procedure The default value of this parameter is 1 5 A 2 72 real mix_spin_amp The mixing amplitude for the spin density in the density mixing procedure The default value of this parameter is 2 0 2 73 real mix_spin_gmax The maximum g vector at which the spin density is mixed in the density mixing procedure The default value of this parameter is 1 5 A7 36 2 74 real mix_cut_off_energy This determines the extent of the grid used for mixing old and new densities Density components with wave vectors corresponding to energies higher than this will not be mixed The default value is of this parameter is cut_off_energy 2 75 real mix_metric_q This determines the metric within the density mixing scheme A weighting factor is used when evaluating scalar products of densities q mix_metric_q F 3 q The default value of this parameter is 1 resulting in an appropriate value being set by the density mixing algorithm 2 76 logical popn calculate This indicates if a population analysis should be performed on the final ground state of the calculation The default value of this paameter is TRUE 2 77 real popn bond cutoff This is the maximum distance between two atoms for which a bond population will be output when performing a population analysis The default value of this parameter is 3 2 78 logical pdos_calculate_weights This indicates if the weight of each band in each localised orb
16. used The default value of this parameter is Default 29 2 31 character opt_strategy This parameter determines the optimisation strategy used where multiple strategies may be used for an algorithm with differing costs in terms of memory usage or performance Possible values are e Speed Use the optimisation strategy which maximises performance at the cost of additional mem ory usage e Default Use the optimisation strategy that balances performance and memory usage e Memory Use the optimisation strategy which minimises memory usage at a cost of decreased performance 2 32 character xc_functional The functional to use when calculating the exchange correlation potential Possible values are e LDA Local Density Approximation e PW91 Perdew Wang 91 GGA e PBE Perdew Burke Ernzerhof e RPBE Revised Perdew Burke Ernzerhof e HF Hartree Fock e SHF Screened Hartree Fock e EXX Exact exchange e SX Screened exchange e ZERO No exchange correlation potential e HF LDA LDA with exchange contribution replaced by Hartree Fock e SHF LDA LDA with exchange contribution replaced by screened Hartree Fock e EXX LDA LDA with exchange contribution replaced by exact exchange e SX LDA LDA with exchange contribution replaced by screeened exchange The default value of this parameter is LDA 2 33 character pspot_nonlocal_type This controls the representation of the non local part of the pseudopotentia
17. used as a backup and restored using the elec_restore_file parameter If this parameter is set to NULL no backup wavefunction will be written The default wave of this parameter is seedname wvfn 2 66 integer num_dump_cycles The number of SCF cycles between wavefunction dumps If num_dump_cycles lt 0 no wavefunction dumps will be performed The default value of this parameter is 5 2 67 character len file_maxpath elec_restore_file The wavefunction and density will be restored from this file on first call to electronic minimisation The basis set and distribution must be unchanged from the run in which the electronic file was written If this parameter is set to NULL the wavefunction and density will not be read The default value of this parameter is NULL 2 68 character mixing_ scheme This determines the mixing scheme to be used in the density mixing procedure The possible values are Kerker Linear Broyden Pulay The default value of this parameter is BROYDEN 2 69 integer mix_history_length The maximum number of densities to store in the history used in the density mixing procedure The default value of this parameter is 7 2 70 real mix_charge_amp The mixing amplitude for the charge density in the density mixing procedure The default value of this parameter is 0 8 2 71 real mix_charge_gmax The maximum g vector at which the charge density is mixed in the density mixing
18. which have a separate copy for each MPI process with rank nnnn labelled wvfn nnnn and err nnnn respectively The major output files are 3 1 castep The main output file is called seedname castep and contains all major data describing a run all significant results computed for the task selected and progress information The amount of logging information included in this file is controlled by the param eter IPRINT 3 2 err nnnn Every MPI process writes a file named seedname err nnnn where nnnn is the MPI rank Any fatal error messages which cause an abnormal termination of a run are written to these files This is the first place to look if a run appears to have terminated prematurely 3 3 check The check file is a Fortran unformatted ie binary file written at the end of a successful single point energy calculation and periodically throughout a geometry optimization molecular dynamics run It serves as a complete record of all information evaluated so far during a run including the ground state kohn sham orbitals the charge density on the FFT grid and any quantities including the fermi energy forces stresses unit cell during optimization or MD The seedname check file may be read by Accelrys Materials Sudio 3 0 or by the utilities in the New_Code Source Tools directories for analysis 45 A run may also be continued from a seedname check file in the case where a run which was interrupted or it is desired to continue w
19. 34 character len 20 efield_ignore_molec_modes This string indicates the number of modes to ignore translational and rotational when calculating the ionic contribution to the permittivity and polarizability Possible values are e CRYSTAL The 3 lowest modes are ignored e MOLECULE The lowest 6 modes are ignored 44 e LINEAR_MOLECULE The lowest 5 modes are ignored The default value of this parameter is CRYSTAL 2 135 Pseudopotentials CASTEP supports several different pseudpotential file formats distinguished by a filename suffix The name of the file should appear following the chemical symbol of the element in a BLOCK SPECIES_POT in the cel1 file usp Vanderbilt ultrasoft pseudopotentials usp Vanderbilt ultrasoft pseudopotentials with a pseudocore charge density recpot Norm conserving potential in the old CASTEP format DAT TM potential files generated by atm kbconv Toullier Martins Froyen If a real space application of the pseudopotential projectors is required pspot_nonlocal_type real in seed param then the real space projectors are read from a file named seed realpot This may be generated using Accelrys Inc s Cerius 2 or materials Studio software 3 output files Like the input files all CASTEP 3 02 output files take the form seedname extn Mostly the output files are identical between serial and MPI parallel run cases The exceptions are the wavefunction and diagnostic error files
20. 7 integer phonon_max_cg_steps The maximum number of conjugate gradient minimisation steps in one cycle of the phonon linear response minimiser The default value of this parameters is 20 2 118 real phonon_energy_tol The tolerance for accepting convergence of the second order energy in an phonon linear response minimi sation The default value of this parameter is the value of elec_energy_tol 42 2 119 integer phonon_convergence_win The second order energy must lie within phonon _energy _tol for the last phonon_convergence_win iterations for the convergence criteria to be met in the phonon linear response minimiser The value of phonon_convergence_win must be greater than or equal to 2 The default value of this parameter is 2 2 120 character len 8 phonon_preconditioner The preconditioner to use in the phonon minimisation algorithm Allowed values are e TPA e RTPA The default value for this parameter is TPA 2 121 logical phonon use kpoint_symmetry If TRUE then for each phonon q vector perform the linear response calculation using the irreducible k point set of the reduced symmetry If false use the complete fully symmetric k point set The default value of ths parameter is TRUE 2 122 character len 20 phonon_method This determines the method used to calculate the elements of the dynamical matrix Possible values are e FINITEDISPLACEMENT A finite displacement method will be used to n
21. CASTEP user guide Keith Refson CCLRC Rutherford Appleton Laboratory Chilton Didcot OXON OX12 0QX September 7 2004 1 Introduction CASTEP is an ab initio density functional theory computer code using a plane wave basis set and pseudpotentials It is written in Fortran 90 and may be compiled for execution on either serial or parallel computers using the MPI communications interface CASTEP 2 2 3 02 onwards is a complete re implementation from scratch and shares no code with the older code of the same name somewhat confusingly numbered CASTEP 4 2 Input and output file formats are not compatible with CASTEP 4 2 This guide is still under construction and when finished will descript the capabilities input files output formats and running instructions for CASTEP 3 02 and later version It is not a reference on density functional theory or plane wave methods and will presume that the reader is familiar with the theory and practice of plane wave methods See references 7 6 2 1 8 4 3 for an introduction of the theory and methods used in CASTEP There is now an excellent book on the subject by Richard Martin 5 and an accompanying website http electronicstructure org 1 1 Capabilities of CASTEP Castep can perform Total energy calculations on a supplied crystal structure single point energy geometry optimization including simultaneous optimization of cell and internal co ordinates molecular dynamics in NVE and
22. ELD_CALC_ION_ PERMITTIVITY EFIELD_IGNORE_MOLEC_MODES I efield_max_cycles efield_max_cg_steps efield_energy_tol efield_convergence_win efield_calc_ion_ permittivity efield_ignore_molec_modes The maximum number of cycles in the minimisation algorithm The maximum number of conjugate gradient steps in a cycle of the efield LR min imiser The convergence tolerance for the efield LR minimiser in units of force constant The number of over which convergence of the efield LR minimiser is assessed Calculate the ionic permit tivity when performing an efield calculation Indicates if lowest modes should be ignored for molecules PHONON_CONST_BASIS L Deprecated No longer used Table 17 Parameter file keywords controlling electric field linear response calculations and deprectaed keywords Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string 26 2 7 character len file_maxpath continuation The model file from which the job will be continued If not a continuation this parameter should be NULL If the keyword CONTINUATION is set to DEFAULT not case sensitive this parameter will be set to seedname check The default value of this parameter is NULL 2 8 character len file_maxpath reuse The model file from which data will be read to initialise a new c
23. ERATE If this keyword is persent in the cell the highest symmetry group that applies to the structure of the cell will be found and the corresponding symmetry operations generated SYMMETRY_TOL R units This parameter is the tolerance within which symmetry will be considered to be satisfied If an ion is found within this distance of its symmetric position the symmetry will be considered to be satisfied units specifies the units in which the tolerance is defined If not present the default is A 2 2 6 Constraints The movement of ions or the unit cell during a relaxation or molecular dynamics run may be constrained The constraints on the ionic motion may by specified as a set of linear constraints Each constraint is specified as a series of coefficients a j such that num_species num_ions_in_species k 3 J J Qijk ionic_positions i j Kk constant k 1 j 1 i 1 The change in the shape of the unit cell may also be constrained using the keyword CELL CONSTRAINTS The special case of constraining the centre of mass of the ions to remain fixed is supported by a logical keyword FIX COM Also all ionic positions or cell parameters may be fixed by specifying the keywords FIX_ALL_IONS or FIX_ALL_CELL to be TRUE respectively If no ionic or cell constraints are specified in the cell definition file the default is to fix the centre of mass BLOCK IONIC_CONSTRAINTS Tr CCCis is Int Ru Riz Rik I gt CCC os L2s Ing Roi R R k ZENDBLOC
24. IC_MINIMISER are e SD 10 e CG 1 e RMM DIIS 1 If keyword ELECTRONIC_MINIMISER is not present in the parameter file the default value will be 1 33 2 52 integer max_cg_steps The maximum number of conjugate gradient steps in an SCF cycle If not explicitly set in the parameter file the value of this parameter depends on the value of the key word ELECTRONIC_MINIMISER The values of this parameter for each value of ELECTRONIC_MINIMISER are e SD 0 e CG 4 e RMM DIIS 2 If keyword ELECTRONIC_MINIMISER is not present in the parameter file the default value will be 4 2 53 integer max_diis_steps The maximum number of RMM DIIS steps in an SCF cycle If not explicitly set in the parameter file the value of this parameter depends on the value of the key word ELECTRONIC_MINIMISER The values of this parameter for each value of ELECTRONIC_MINIMISER are e SD 0 e CG 0 e RMM DIIS 7 If keyword ELECTRONIC_MINIMISER is not present in the parameter file the default value will be 0 2 54 character metals_method This determines the method used in calculations on metals The possible values are e NONE no special treatment of metals e DM metals treated by density mixing e EDFT metals treated by Ensemble DFT These methods may be useful in the treatment of non metalic systems in some cases If fix_occupancy FALSE the default value of this parameter is EDFT otherwise it is NONE 2 55 real elec_energy_to
25. K IONIC_CONSTRAINTS The first element on each line is an integer specifying the number of the constraint being specified The second entry is either the symbol or atomic number of the species of the ion to which this constraint applies The third element is the number of the ion within the species The ordering of the ions in a species is the order in which they appear in the POSITIONS_FRAC or POSITIONS_ABS block in the cell definition file The final three numbers are real numbers representing the coefficients of the Cartesian coordinates of the ionic position in the constraint sum All coefficients in the sum not explicitly specified will be zero On reading this data the matrix of ionic constraints will be orthogonalised BLOCK CELL_CONSTRAINTS ZENDBLOCK CELL_CONSTRAINTS The first three entries relate to the magnitude of the three lattice vectors a b c and the second set of three entries to the angles a 8 y If the value of the entry corresponding to a magnitude or angle is zero this quantity will remain fixed If two or three entries contain the same integer the corresponding quantities will be constrained to have the same value If a positive integer greater than 0 occurs in entries 1 through 3 the same integer cannot occur in entries 4 through 6 as this would imply that a vector length and angle must have the same value 10 2 2 7 Species Characteristics The mass of a species the pseudopotential which represents the ion and the size
26. NVT ensembles and harmonic phonon frequencies and eigenvectors using density functional perturbation therory e Pseudopotentials Norm conserving and Vanderbilt Ultrasoft pseudopotentials Built in pseudopotential generator experimental Non linear core charge correction e Exchange and Correlation Functionals LDA Local Density Approximation PW91 Perdew Wang 91 GGA PBE Perdew Burke Ernzerhof RPBE Revised Perdew Burke Ernzerhof HF Hartree Fock SHF Screened Hartree Fock EXX Exact exchange SX Screened exchange ZERO No exchange correlation potential HF LDA LDA with exchange contribution replaced by Hartree Fock SHF LDA LDA with exchange contribution replaced by screened Hartree Fock EXX LDA LDA with exchange contribution replaced by exact exchange X LDA LDA with exchange contribution replaced by screeened exchange e Electronic Minimization all bands conjugate gradient minimizer for insulators Density mixing minimizer for metals Ensemble DFT for metals Double grid for charge densities Spin polarized or unpolarized paired electron calculations e Geometry Optimization Robust BFGS optimizer with line search Internal Co ordinates optimizer for molecular systems Combined atomic cell optimization using augmented Hessian Accurate variable cell geometry optimization at fixed cutoff Damped MD e Mole
27. ONS_ABS units CCC Rix Riy Riz MAGMOM mm CCC4 I2 Ro Ray Ro MAGMOM mmzy ENDBLOCK POSITIONS_ABS The first entry on a line is the symbol or atomic number of the ionic species as for POSITIONS FRAC The next three entries are real numbers representing the position of the ion in Cartesian coordinates units specifies the units in which the positions are defined If not present the default is A The optional flag MAGMOM is defined above under POSITIONS_FRAC For transition state searches structures for the product and intermediate geometry of the system may be input in blocks POSITIONS_FRAC_PRODUCT and POSITIONS_FRAC_INTERMEDIATE respectively in fractional coordinates or POSITIONS_ABS_PRODUCT and POSITIONS_ABS_INTERMEDIATE respectively in absolute coordinates The format of these blocks is the same as POSITIONS_FRAC and POSITIONS_ABS as appropriate The reactant structure will be taken from the main positions block 2 2 3 Ionic Velocities The initial ionic velocities may be specified in Cartesian coordinates in a cell definition file BLOCK IONIC_VELOCITIES units CCC L Viz Viy Viz CCC4 I2 Vox Vay Voz ZENDBLOCK IONIC_VELOCITIES The first entry on a line is the symbol or atomic number of the ionic species The correct symbol will be looked up for the atomic species if the atomic number is specified A symbol can have a maximum of three characters The next three entries are real numbers representing the velocity o
28. SPIN may be defined together but conflicting values must not be defined eg NELECTRONS and CHARGE f Only one of NBANDS NEXTRA_BANDS and PERC_EXTRA_BANDS may be present in a parameter file 18 Keyword Type Corresponding Description Variable Electronic Minimisation Parameters Continued ELEC_CONVERGENCE_WIN I elec_convergence_win The number of over which conver gence of the minimiser is assessed MAX_SCF_CYCLES I max_scf_cycles The maximum number of SCF cy cles in an electronic minimisation SPIN_FIX I spin_fix The number of iterations to fix the spin during an electronic relaxation If spin _fix lt 0 the spin is fixed permanently Only used if fix_occupancy is FALSE FIX_OCCUPANCY L fix_occupancy Fix the occupancies of the bands ie treat as a zero temperature insula tor SMEARING_SCHEME S smearing_scheme The smearing scheme to use for the fermi surface of a metal See Section 2 61 for details SMEARING_WIDTH P smearing width The width of the smearing of the fermi surface of a metal EFERMI_TOL P efermi_tol The tolerance within which to find the fermi energy of a metal NUM_OCC_CYCLES I num_occ_cycles The number of occupancy minimisa tion cycles per electronic step during ensemble DFT minimisation ELEC_DUMP_FILE S elec_dump_file The filename of the file into which to periodically dump the wavefunction and density during electronic min imisation as a backup NUM DUMP_CYCLES I num_dump_cycles The number of SCF cycles
29. TRAINTS B no constraints The constraints on the motion of ions during relaxation or MD FIX_ALL_IONS L FALSE Constrain all ionic positions to remain fixed FIX_ALL_CELL L FALSE Constrain all cell parameters to remain fixed FIX_COM L TRUE Constrain the centre of mass of the ions to remain fixed CELL_CONSTRAINTS B no constraints The constraints on changes in the cell shape during relaxation or MD SPECIES MASS B atomic mass The masses of the ionic species SPECIES POT B see text The names of the pseudopotentials as sociated with each species SPECIES_LCAO_STATES B see text The number of angular momentum states to use in the LCAO basis set for this species when performing pop ulation analysis EXTERNAL_PRESSURE B no pressure The external pressure tensor Table 3 The keywords which may be specified in the cell definition file Full details of their definitions may be found in Section Argument types are represented by B for block data P for a physical value L for a logical value D for a keyword that may simply be defined present or not V for a real vector and W for an integer vector Here Rj is the x component of the first lattice vector Ra is the y component of the second lattice vector etc units specifies the units in which the lattice vectors are defined If not present the default is A BLOCK LATTICE_ABC units AENDBLOCK LATTICE_ABC Here Ra is the value of a R4 is the value of y etc If the lattice is specified
30. _TOL tssearch_method tssearch_lstqst_protocol tssearch_qst_max_iter tssearch_cg_max_iter tssearch_force_tol tssearch_disp_tol Determines the method used in the transitionstate search algorithm Determines the protocol used when performing and LST QST search The maximum number of it erations in a QST search The maximum number of conjugate gradients itera tions in the transistion state search The force tolerance within which the transition state will be found The displacement tolerance within which the transition state will be found Table 15 Parameter file keywords controlling optics and transition state searches Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string Only one of OPTICS_NBANDS OPTICS_NEXTRA_BANDS and OPTICS_PERC_EXTRA_BANDS may be present in a parameter file 24 Keyword Type Corresponding Variable Description Phonon PHONON_MAX_CYCLES PHONON_MAX_CG_STEPS PHONON_ENERGY_TOL PHONON_CONVERGENCE_WIN PHONON_PRECONDITIONER PHONON_USE_KPOINT_ SYMMETRY PHONON_METHOD PHONON_DOS_SPACING PHONON_FINITE_DISP PHONON_CALC_LO_TO_ SPLITTING PHONON_SUM_RULE CALCULATE_BORN_CHARGES BORN_CHARGE_SUM_RULE phonon_max_cycles phonon_max_cg_steps phonon_energy_tol phonon_convergence_win phonon_preconditioner phonon_use_kpoint_ symm
31. able defaults defined in tables 1 to 3 will be chosen for other variables not specified A list of keywords for the cell file is given in Tables 1 to 3 The definitions of the keywords are given in more detail in the following subsections For the purposes of the following definitions all variables represented by R are defined to be real numbers those represented by I are defined to be integers and those represented by C are characters 2 2 1 Cell Lattice Vectors The cell lattice vectors may be specified in Cartesian coordinates or in terms of the lattice vector magni tudes and the angles between them a b c a 3 7 Only one of LATTICE_CART and LATTICE_ABC may occur in a cell definition file The definitions of these keywords are as follows BLOCK LATTICE_CART units Rie Ruy Riz Row Ray Rez Rz R3y R3z ENDBLOCK LATTICE_CART Keyword Type Default Description LATTICE_CART LATTICE_ABC POSITIONS FRAC POSITIONS_ABSt POSITIONS FRAC PRODUCT POSITIONS_ABS_ PRODUCTT POSITIONS_FRAC INTERMEDIATE POSITIONS_ABS INTERMEDIATET IONIC_VELOCITIES KPOINT_LIST KPOINT_MP_GRID t KPOINT_MP_ SPACING KPOINT_MP_OFFSET random The cell lattice vectors in Cartesian co ordinates The cell lattice vectors specified in a b c a 3 y format The positions of the ions in fraction coordinates with respect to the lattice vectors The positions of the ions in absolute co ordinates T
32. alculation If no file is to be used this parameter should be NULL If the keyword REUSE is set to DEFAULT not case sensitive this parameter will be set to seedname check The default value of this parameter is NULL 2 9 character len file_maxpath checkpoint The file to which checkpoint data will be written The default value of this parameter is seedname check 2 10 character task This defines the calculation performed There are seven valid values of this parameter e SinglePoint e BandStructure Geometry Optimization MolecularDynamics e Phonon e Efield e Phonon Ffield e Optics e TransitionStateSearch The default value of this parameter is SinglePoint 2 11 logical calculate _stress If TRUE this forces the calculation of the stress tensor for any task Otherwise the stress will only be clalculated if required e g during a cell geometry optimisation with cell relaxation The default value of this parameter is FALSE 2 12 integer runtime This specifies the maximum run time for the job If run_time is greater than zero the job will if possible exit cleanly before this time in seconds has elapsed leaving as little unused time as possible Clean termination before run_time cannot be guaranteed and the shortest operation which can be timed is an electronic minimisation or a single molecular dynamics geometry optimisation or phonon step If run_time lt 0 no time l
33. ar P bar aas x 105 Megabar Mbar P mbar E x 101 Bohr 1 1 Bohr 1 L 1 bohr A Metre 1 1 m 1 L 1 m 4 Nanometre 1 1 nm 1 L 1 nm E E Angstrom 1 1 A 1 L 1 ang A x 1910 Hartree Bohr Ha Bohr 2 F L ha bohr 2 1 ev Angstrom ev A 2 F L ev ang 2 ars x 101 Newton metre N m F L n m air dyne centimetre dyne cm F L dyne cm ara x 1073 Bohr Bohr 3 Vol bohr 3 1 Metre m 3 Vol m 3 men Centimetre cm 3 Vol cm 3 12 x 1076 Nanometre nm 3 Vol nm 3 222 x 10 7 Angstrom A 3 Vol ang 3 222 x 10730 Table 5 The units of velocity pressure reciprocal length force constant and volume in which physical data may be input and output The dimensions for which unit conversion is provided are as follows L length M mass T time C charge E energy F force V velocity P pressure 1 L reciprocal length F L Force constant and Vol Volume The default for each dimension is indicated by a The relative values are given in terms of SI fundamental constants 14 Keyword Type Corresponding Description Variable General Parameters COMMENT S comment A comment string that may be used to lable the output IPRINT I iprint Controls the verbosity of output STOP D If present execution will halt the next time the parameter file is read CONTINUATION S continuation The model file from which to continue a calculation REUSE S reuse The model file from which to read data to initialise a new
34. arameter is ps 2 19 character charge_unit The units in which charges will be output The possible values of this parameter are listed in Table 4 The default value of this parameter is e 2 20 character energy_unit The units in which energies will be output The possible values of this parameter are listed in Table 4 The default value of this parameter is ev 2 21 character force_unit The units in which forces will be output The possible values of this parameter are listed in Table 4 The default value of this parameter is ev ang 2 22 character velocity unit The units in which pressures will be output The possible values of this parameter are listed in Table 5 The default value of this parameter is ang ps 28 2 23 character pressure_unit The units in which pressures will be output The possible values of this parameter are listed in Table 5 The default value of this parameter is gpa 2 24 character inv_length_unit The units in which inverse lengths will be output The possible values of this parameter are listed in Table 5 The default value of this parameter is 1 ang 2 25 character frequency_unit The units in which frequencies will be output The possible values of this parameter are listed in table 4 and are the same as those in which energies may be output The default value of is parameter is CM 1 2 26 character len 30 force_constant_u
35. ate search Possible values of this parameter are e LSTMaximum e Halgren Lipscomb e LST Optimization e CompleteLSTQST e QST Optimization The default value of this parameter is LSTMAXIMUM 2 112 integer tssearch_qst_max_iter The maximum number of QST iterations during an LST QST transition state search This parameter must be greater than zero The default value of this parameter is 5 2 113 integer tssearch_cg max_iter The maximum number of conjugate gradients steps during an LST QST transition state search This parameter must be greater than zero The default value of this paramter is 20 2 114 real tssearch_force_tol The tolerance for the ionic forces to accept convergence during a transition state search The maximum ionic force must be less than this value for the convergence criteria to have been met This parameter must be greater than zero The default value of this parameter is 0 005 Hartree Bohr 2 115 real tssearch_disp_tol The tolerance for the ionic displacement to accept convergence during a transition state search The maximum ionic displacement during the last iteration must be less than this value for the convergence criteria to have been met This parameter must be greater than zero The default value of this parameter is 0 01 Bohr 2 116 integer phonon_max_cycles The maximum number of cycles in the phonon linear response minimiser The default value of this parameter is 50 2 11
36. cular Dynamics NVE and NVT ensemble MD simulation Accurate variable cell MD at fixed cutoff Nose Hoover chain thermostat e Transition State Searching e Density Functional Linear Response Phonon Spectra and Dispersion Curves Dielectric permittivities low frequency and optical Born effective charges LO TO splitting 2 Input files To run CASTEP requires two input files plus one or two additional pseudopotential files for every element included The filenames of both input and output files begin with a common root known as a seed making it easy to distinguish the files belonging to a particular run To run it is merely necessary to execute the command either interactively or from a shell script from a batch queue castep seed where we assume that the executable is named castep and is found somewhere in the shell path The two input files are seed cell which describes the simulation cell and its contents and seed param which describes the type of run to be performed and any options which may be required In fact the seed param may be omitted entirely in which case a single point energy calculation with default parameters is performed Data is input in a keyword lt value gt fashion and input is independent of the ordering of the input file The value may be preceded by or a blank space or tab The keywords are case insensitive e g unitCell is equivalent to UnItceLL and pu
37. e calculated Only used if metals_method EDFT EXCITED_STATE_SCISSORS P excited_state_scissors Apply a correction to the band gap Electronic Minimisation Parameters ELECTRONIC_MINIMISER S The method of electronic minimisation to use Possible values SD CG RMM DIIS MAX_SD_STEPS I max_sd_steps The maximum number of steepest de scent steps in an SCF cycle MAX_CG_STEPS I max_cg_steps The maximum number of conjugate gradient steps in an SCF cycle MAX_DIIS_STEPS I max_diis_steps The maximum number of RMM DIIS steps in an SCF cycle METALS_METHOD S metals_method The method to be used for the treat ment of metals or partial occupancies See Section 2 54 for possible values ELEC_ENERGY_TOL P elec_energy_tol The convergence tolerance for finding the ground state energy as an energy per atom ELEC_EIGENVALUE_TOL P elec_eigenvalue_tol The convergence criteria for an eigen value during a band by band minimisa tion Table 9 Parameter file keywords controlling electronic and electronic minimisation parameters Argu ment types are represented by I for a integer R for a real number P for a physical value L for a logical value D for a keyword that may simply be defined present or not and S for a text string Groups of parameters which are mutually exclusive are indicated by integers in the Group column Pairs of parameters defining the number of electrons and the total spin eg NUP and NDOWN or CHARGE and
38. e keyword SPIN_ POLARIZED is present this determines the value of nspins If SPIN POLARIZED FALSE then nspins 1 otherwise nspins 2 Default 1 if nup ndown otherwise 2 2 48 integer nbands The maximum number of bands at any k point and spin If NBANDS is present in the parameter file the value of nbands is determined by this keyword If NEXTRA_BANDS is specified nbands max nup ndown NEXTRA_BANDS If PERC_LEXTRA_BANDS is specified nbands max nup ndown x 1 PERC EXTRA BANDS Y If NBANDS NEXTRA_BANDS and PERC_EXTRA_BANDS have not been specified and fix_occupancy TRUE then nbands max nup ndown If fix_occupancy FALSE or elec_temp gt 0 the default value of nbands will be the ceiling of the default value multiplied by 1 2 2 49 real elec_temp The electron temperature for which to calculated results This will only be used if metals_method EDFT The default value of this parameter is 0K 2 50 real kind dp excited_state_scissors Apply the scissors operator to add an offset to conduction band eigenvalues as empirical correction for LDA GGA underestimation of band gaps The default value of this paramter is 0 0 eV 2 51 integer max_sd_steps The maximum number of steepest descent steps in an SCF cycle If not explicitly set in the parameter file the value of this parameter depends on the value of the key word ELECTRONIC_MINIMISER The values of this parameter for each value of ELECTRON
39. es associated with the chosen level of accuracy for the pseudopotentials used in the calculation This will be set by the ion_initialise subroutine If neither BASIS PRECISION nor CUT OFF ENERGY are defined in the parameter file the default cut off energy is that associated with the FINE level of accuracy for the pseudopotentials in the calculation If the CUT_OFF_ENERGY keyword is not present in the input file this parameter will be set to 1 Ha until the correct value is assigned by the ion_initialise subroutine 2 37 real grid_scale The size of the standard grid as a multiple of the diameter of cut off sphere The default value will be 1 75 2 38 real fine_gmax The fine grid will be chosen to be of the minimum size such that all g vectors with g lt fine_gmax are included in the fine grid If not specified fine_gmax will be set to 1 ag resulting in the fine and standard grids being identical In this case the correct value of fine_gmax will be set by the subroutine basis_initialise 1 2 39 integer finite_basis_corr This determined whether finite basis set corrections to the energy and stress will be performed Possible values are e 0 No correction performed e 1 Correction performed with user provided estimate of Tet e 2 Correction performed with automatic calculation of Tet The vlaue of this parameter is defined by the string parameter file keyword FINITE_BASIS_CORR as follows e NONE 0 e MANUAL
40. es the directions in which the gamma point will be approached when calculating the non analytic terms of the LO TO splitting Each line in this block will consist of a 3 vector specifying a direction in the basis of reciprocal lattice vectors If this keyword is not present the default will be a single vector determined as follows 1 If the gamma point is q 0 and there is an successor kpoint qi in the list then it is qj41 2 Otherwise if the gamma point is q 0 and there is an predecessor kpoint qi 1 in the list then it is di 1 3 Otherwise i e a Gamma point only calculation the a axis of the reciprocal cell For backwards compatibility the kewords beginning BS_ KPOINT _ are synonyms for BS_KPOINT_ and similarly those beginning PONON_KPOINT_ are synonymous with PHONON_KPOINT 2 2 5 Cell Symmetry The symmetry of the cell is represented as a series of symmetry operations under which the unit cell is invariant Each operation is represented as a 3 x 3 array If no symmetry is specified in the cell definition file the default is for no symmetry to be applied BLOCK SYMMETRY_OPS Ri Ra Ra Rig R 2 R32 R 3 Rog R33 T Th T3 Ry Ra Rs Rig Roe R32 R 3 Rog R33 T Th B AENDBLOCK SYMMETRY_OPS Each of the first three lines contains 3 entries representing a row of a 3 x 3 array These represent one symmetry rotation The three entries on the following line contain the translation associated with this rotation SYMMETRY_GEN
41. etry phonon_method phonon_dos_spacing phonon_finite_disp phonon_calc_lo_to_ splitting phonon_sum_rule calculate_born_charges born_charge_sum_rule The maximum number of cycles in the minimisation algorithm The maximum number of conjugate gradient steps in a cycle of the phonon LR minimiser The convergence tolerance for the phonon LR min imiser in units of force con stant The number of over which convergence of the phonon LR minimiser is assessed The preconditioner to use in the minimisation algorithm Use the irreducible k point set of the reduced symme try for phonon calculations The method to use to calcu late the dynamical matrix The resolution of the phonon density of states calculation The amplitude of the per turbation used in a finite displacement phonon calcu lation Whether to calculate the NS term of the dynamical ma trix Enforce phonon sum rule at q 0 Calculate Born effective charges N B Also affects Efield calculations Enforce Born charge sum rule Table 16 Parameter file keywords controlling phonon calculations Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string 25 Keyword Type Corresponding Variable Description Electric Field Linear Response EFIELD_MAX_CYCLES EFIELD_MAX_CG_STEPS EFIELD_ENERGY_TOL EFIELD_CONVERGENCE_WIN EFI
42. f the ion in Cartesian coordinates units specifies the units in which the positions are defined If not present the default is A ps If this keyword is not present and a molecular dynamics calculation is performed the ionic velocities will be randomly initialised with the appropriate temperature 2 2 4 Brillouin Zone Sampling K points N B in the following section the keywords the prefixes KPOINT_ and KPOINTS_ are synonymous KPOINT_ is the preferred usage The k points at which the Brillouin zone is to be sampled during a self consistent calculation to find the electronic ground state may be defined either by specifying a list of k points or a Monkhorst Pack grid in terms of the dimensions of the k point mesh or a minimum k point density The origin of the Monkhorst Pack grid may be offset by a vector from the origin of the Brillouin zone If no k points are specified the default will be a Monkhorst Pack grid with a maximum spacing of 0 1A and no offset of the origin The KPOINT_LIST KPOINT_MP_GRID and KPOINT_MP_SPACING keywords are mutually ex clusive KPOINT_MP_OFFSET may be specified in combination with either KPOINT_MP _GRID or KPOINT_MP_SPACING BLOCK KPOINT_LIST Ris Riy Rik Riu Roi Ro Rok Row ZENDBLOCK KPOINT_LIST The first three entries on a line are the fractional positions of the k point relative to the reciprocal space lattice vectors The final entry on a line is the weight of the k point relative to the othe
43. h indicates whether the occupancies of the bands should be fixed i e if the system should be treated as a zero temperature insulator The default value of this parameter is FALSE 2 61 character smearing scheme This indicates the smearing scheme to use if treating the system as a metal This is only used if fix_occupancy FALSE The valid options for this parameter are Gaussian GaussianSplines FermiDirac HermitePolynomials ColdSmearing The default value for smearing_scheme is Gaussian 2 62 real smearing _width The width of smearing of the Fermi surface if treating the system as a metal This is only used if fix_occupancy FALSE The default value of this parameter is 0 2 eV 2 63 real efermi_tol The tolerance within which the Fermi energy is calculated for a metallic system or finite temperature insulator This is only used if fix_occupancy FALSE or elec_temp gt 0 The default value of this parameter is 0 1 x elec_eigenvalue_tol 2 64 integer num_occ_cycles The number of occupancy cycles performed for each wavefunction minimisation step during an Ensemble DFT run This is only used if fix_occupancy FALSE or elec_temp gt 0 and metals_method EDFT The default value of this parameter is 6 35 2 65 chracter len file maxpath elec_dump_file The filename of the file into which to periodically dump the wavefunction and density during electronic minimisation This may be
44. he positions of the ions in the product structure for a transition state search in fraction coordinates with respect to the lattice vectors The positions of the ions in the product structure for a transition state search in absolute coordinates The positions of the ions in an estimate of the intermediate structure for a tran sition state search in fraction coordi nates with respect to the lattice vectors The positions of the ions in an estimate of the intermediate structure for a tran sition state search in absolute coordi nates The velocities of the ions in Cartesian coordinates A list of k points in the Brillouin zone with associated weights The k points defined as a Monkhorst Pack grid by specifying the grid dimen sions in each direction The k points as a Monkhorst Pack grid by specifying the maximum distance between k points The offset of the origin of the Monkhorst Pack grid in fractional coor dinates relative to the reciprocal lattice vectors Table 1 The keywords which may be specified in the cell definition file Full details of their definitions may be found in Section Argument types are represented by B for block data P for a physical value L for a logical value D for a keyword that may simply be defined present or not V for a real vector and W for an integer vector Only one of LATTICE_CART and LATTICE_ABC may be present in a cell file f Only one of POSITIONS_FRAC and POSITIONS_ABS
45. imit will be imposed on the run The default value of this parameter is 0 27 2 13 integer num_backup_iter The number of geometry optimisation or MD iterations or Phonon q points between writing backup restart files The default value of this parameter is 5 unless the user has explicitly set backup_interval to 0 in the _param file indicating an infinite interval between backups in which case no backups will be performed 2 14 integer backup_interval If a potential backup pooint is reached and more than backup_interval seconds have elapsed since the last backup a backup will be forced If backup_interval is 0 no timed backups will be performed However backups will still take place every num_backup_iter iterations The default value of this parameter is 0 2 15 logical print_clock Flag to indicate if timing information should be printed during the run The default value of this parameter is TRUE 2 16 character length_unit The units in which lengths will be output The possible values of this parameter are listed in Table 4 The default value of this parameter is ang 2 17 character mass_unit The units in which masses will be output The possible values of this parameter are listed in Table 4 The default value of this parameter is amu 2 18 character time_unit The units in which times will be output The possible values of this parameter are listed in Table 4 The default value of this p
46. ital should be calculated on the final ground state of the calculation in order to allow a partial density of states analysis The default value of this parameter is FALSE 2 79 integer bs_max_iter The maximum number of iterations to perform when performing a band structure calculation The default value of this parameter is 60 2 80 real bs_eigenvalue_tol The tolerance for accepting convergence of a single eigenvalue during a band structure calculation The default value for this parameter is 1 x 107 eV 2 81 integer bs_max_cg_steps The maximum number of conjugate gradient steps to perform during a band structure calculations before resetting to the steepest descent direction The default value of this parameter is 4 2 82 integer bs_nbands The number of bands at each k point when performing a band structure calculation If BS_NBANDS is present in the parameter file the value of bs_nbands is determined by this keyword If BS NEXTRA_BANDS is specified bs nbands max nup ndown BS NEXTRA_BANDS If BS PERC_EXTRA_BANDS is specified bs nbands max nup ndown x 1 85 PERC_EXTRA_BANDS _ The default value of this parameter is 3 x nbands 37 2 83 character len 15 bs_xc_functional The exchange correlation functional to use for band structure calculations Possible values are e LDA Local Density Approximation e PW91 Perdew Wang 91 GGA e PBE Perdew Burke Ernzerhof e RPBE Revised Perdew Burke Ernzerhof
47. iteria to have been met The default value of this parameter is 0 05 eVA7 38 2 88 real geom_disp_tol The tolerance for the ionic displacement to accept convergence during an ionic relaxation The maximum ionic displacement must be less than this value over geom_convergence_win iterations for the convergence criteria to have been met The default value of this parameter is 0 001 A 2 89 real geom_stress_tol The tolerance for the stress to accept convergence during a cell relaxation The maximum stress compo nent must be less than this value over geom_convergence_win iterations for the convergence criteria to have been met The default value of this parameter is 0 1 GPa 2 90 integer geom_convergence_win The number of geometry optimisation iterations during which the convergence criteria must be met for convergence to be accepted The default value of this parameter is 2 2 91 real geom_modulus_est An estimate of the bulk modulus of the system Used to initialise the Hessian for BFGS geometry optimisation with cell relaxation The default value of this parameter is 500 GPa 2 92 real geom_frequency_est An estimate of the average phonon frequency at the gamma point Used to initialise the Hessian for BFGS geometry optimisation with ionic relaxation The default value of this parameter is 50 THz 2 93 integer md_num_iter The number of molecular dynamics iterations to perform The default value of this parameter i
48. ith a change of parameters This is achieved by setting the parameter CONTINUATION 3 4 wvfin nnnn Upon a successful single point energy calculation the wavefunctions are written to these files one per MPI process This is not the main restart mechanism but it is possible to restart a run using these by setting the parameter ELEC_RESTORE_FILE to the root name i e strip the processor rank The location these are written to is set by parameter ELEC_DUMP_FILE 3 5 bands The bands file is written after a single point energy calculation or bandstructure run and contains the electronic eigenvalues 3 6 phonon A seedname phonon file is written during a phonon linear response calculation and contains a header and the phonon frequencies and eigenvectors for every q point computed 3 7 geom A record of the atomic co ordinates at each geometry optimization iteration are written to the file seedname geom 3 8 md A record of the atomic co ordinates at each molecular dynamics iteration are written to the file seed name md 3 9 Wavefunction paging and Temporary files CASTEP 3 02 may also use a number of Fortran STATUS SCRATCH files during a run In particular the strategy of wavefunction paging may be used This means that the coefficients of a single band and k point are retained in memory at any one time and the others are stored in the temporary disk file This is selected by parameters PAGE_WVFNS and OPT_STRATEGY MEMORY M
49. l The tolerance for accepting convergence of the total energy in an electronic minimisation The default value for this parameter is 1 x 107 eV per atom 2 56 real elec_eigenvalue_tol The tolerance for accepting convergence of a single eigenvalue during band by band minimisation The default value for this parameter is min S 8 to xnun_stons 1 x 10 6 eV Here num_atoms is passed as an argument to parameters_read 2 57 integer elec_convergence_win The total energy or eigenvalue must lie within convergence_tol or elec_eigenvalue_tol respectively for the last elec_energy_win iterations for the convergence criteria to be met The value of elec_convergence_win must be greater than or equal to 2 The default value of this parameter is 3 34 2 58 integer max_SCF_cycles The maximum number of SCF cycles performed in an electronic minimisation The electronic minimi sation will end regardless of whether the convergence criteria have been met after max_SCF_cycles SCF cycles The default value of this parameter is 30 2 59 integer spin_fix The number of electronic iterations for which the total spin is fixed If spin_fix lt 0 the spin will be fixed for the duration of the calculation Only used if fix_occupancy FALSE and spin_polarized TRUE For insulators the spin is fixed regardless of the value of cspin_fix The default value of this parameter is 10 2 60 logical fix_occupancy A logical flag whic
50. l Possible values are e RECIPROCAL reciprocal space non local pseudopotentials e REAL real space non local pseudopotentials The default value of this parameter is RECIPROCAL 2 34 character pspot_beta_phi_type This controls the representation of the non local part of the pseudopotential used for calculation of the lt 3 gt overlaps Possible values are e RECIPROCAL reciprocal space non local pseudopotentials e REAL real space non local pseudopotentials This parameter can only take the value REAL if pspot_nonlocal_type is REAL The default value of this parameter is pspot_nonlocal_type 30 2 35 character basis_precision This specifies the precision of the basis set by choosing the level of convergence of atomic energies with respect to the plane wave cut off energy for the pseudopotentials used in the calculation Options for BASIS_PRECISION are COARSE 1 eV per atom MEDIUM 0 3 eV per atom FINE 0 1 eV per atom PRECISE 1 2x FINE EXTREME 0 01 eV per atom The default value for this parameter is FINE If CUT_OFF_ENERGY is specified in the parameter file this parameter will be set to NULL 2 36 real cut_off_energy This holds the cut off energy for the plane wave basis set being used in the current calculation If the BASIS_PRECISION keyword is defined in the parameter file the cut off energy will be equal to the highest of the cut off energi
51. le if the bs option is given xg Write a script and invoke GRACE to plot data ps Invoke GRACE to plot data and write as a PostScript file eps Invoke GRACE to plot data and write as an encapsulated PostScript EPS file np Do not plot data write a GRACE script bs Read band structure from jj castep or jj bands expt FILE Read experimental data from EXPT and overplot dat Reread standard output from previous run and plot ftol f Set maximum discrepancy tolerance for phonon branch joining v Be verbose about progress cteprouts The directory cteprouts contains a number of PERL programs for interconverting file for mats The calls usually take the form e g xtl2cell seed xtl gt seed cell converts a crystal structure file in the XTL format into a CASTEP 3 02 seed ce11 file The several scripts newtep2zrrz convert CASTEP 3 02 castep output files into various molecular graphics file formats 47 Among the useful programs are newtep2cell which reads a CASTEP output file eg from a geome try optimization and writes the final structure to a seed ce11 file to begin a new run newgeom2dcd newgeom2xyz and newgeom2pdbseq convert the seed geom file from a geometry optimization or MD to a standard trajectory format for animation See the file New Code Source Tools cteprouts README for a complete list and more instructions 5 Migration from CASTEP 4 2 The input files of CASTEP 3 02 have a completely different format fro
52. m those of CASTEP 4 2 However CASTEP 3 02 has all of the capabilities of CASTEP 4 2 and can perform compatible calculations These should give almost identical energies provided that the same pseudopotentials are used The reason for the qualifier almost is that CASTEP 3 02 used the latest CODATA 97 values for the fundamental constants consistently throughout the program Geometry optimization calculations using CASTEP3 02 will often produce slightly different results because and will be able to converge where CASTEP 4 2 did not or converged poorly There are a number of utilities in the directory New_Code Source Tools cteprouts which can be used to migrate a calculation See section 4 for more information In particular 1 The command geom2cell oldseed geom gt newseed cell will convert a CASTEP4 2 geom file into a CASTEP 3 02 ce11 file Because the old geom format contained no information on atom types you must supply these using an environment variable ATOMS For example export ATOMS Si C H geom2cell oldseed geom gt newseed cell indicates that the 3 atoms in oldseed geom are Si C and H in that order 2 The command cst2cell oldseed cst gt newseed cell will convert a CASTEP4 2 cst output file into a CASTEP 3 02 ce11 file This is able to extract more information than geom2ce11 including atom types In both cases the output files will probably not be exactly what is required and will need some minor changes particularl
53. n the sequence of k points In this case the con tinuous path will end at the k point immediately preceding the BREAK keyword and resume at the k point immediately following The path will be open unless the first and last point in the list are iden tical The maximum spacing of the points sampled along each line segment is defined by the keyword BS_KPOINT_PATH_SPACING default value 0 1 A If necessary the actual spacing used may be smaller than this in order to ensure that the length of the line segment is an integer multiple of the spacing between points on that segment Alternatively the k point set for performing a band structure calculation can be specified in the same manner as the main k point set using version of the keywords above with BS_ prepended The same restrictions regarding mutually exclusive keywords apply In this case the k point weight in BS_KPOINT_LIST is optional If ommitted the weights for each k point are assumed to be equal For a phonon spectum calculation the k points may be defined along a path through reciprocal space or a list of k points in the same manner as for a band structure calculation The corresponding keywords are identical to those for the band structure specification with the initial BS replaced by PHONON e g PHONON_KPOINT_ PATH PHONON _KPOINT_ PATH SPACING and PHONON_KPOINT LIST The same restrictions regarding mutually exclusive keywords apply The block keyword PHONON_GAMMA_DIRECTIONS specifi
54. nctuation insensitive unit cell is equivalent to unit cell is equivalent to unitcell Punctuation characters are and _ There are 9 different types of entity which may be defined in the input files String A text string up to file_maxpath characters in length e Integer An integer e Real A real number e Physical A physical quantity of one of the dimensions listed in Tables 4 and 5 e Defined An entry which is either present or absent in the file and takes no value e Boolean A logical value e Real Vector A three vector of real values e Integer Vector A three vector of integer values e Block A block of data to be interpreted by the calling subroutine 2 1 Help facility CASTEP may be invoked as castep help or castep help variable to give brief summary information on an input variable in either the seed cell or seed param files or a class of variable A useful aide memoire if you don t have a copy of this manual handy 2 2 The cell file The cell definition file is a free format keyword driven text file The file defines the initial cell for a calculation The cell lattice vectors ionic positions sampling k points in the Brillouin zone cell symmetry external pressure constraints on motion of the ions or cell the pseudopotentials representing each species and the mass of each species may be defined At the very least the cell lattice vectors and ionic positions must be specified Reason
55. ne which defines the path along which a phonon calculation will be performed Specifies the maximum spacing between k points along the path for which a phonon calculation will be performed A list of k points at which a phonon cal culation will be performed The directions in which the gamma point will be approached for calculation of the LO TO splitting Table 2 The keywords which may be specified in the cell definition file Full details of their definitions may be found in Section Argument types are represented by B for block data P for a physical value L for a logical value D for a keyword that may simply be defined present or not V for a real vector and W for an integer vector Only one of BS_KPOINT_PATH and BS_KPOINT_LIST may be present in a cell file t Only one of OPTICS_KPOINTS_LIST OPTICS_KPOINTS_MP_GRID and OPTICS_KPOINTS_MP_SPACING may be present in a cell file o Only one of PHONON_KPOINT_PATH and PHONON _KPOINT _LIST may be present in a cell file Only one of SYMMETRY_GENERATE and SYMMETRY_OPS may be present in a cell file Keyword Type Default Description SYMMETRY_GENERATE D no symmetry If this is present the highest symmtery group of the cell will found and the cor responding symmetry operations gener ated SYMMETRY_OPS B no symmetry The symmetry operations that apply to the cell SYMMETRY_TOL P 0 01 A The tolerance within which symmetry will be enforced IONIC_CONS
56. nit The units in which force constants will be output The possible values of this parameter are listed in table 5 The default value of this parameter is ev ang 2 2 27 character len 30 volume_unit The units in which volumes will be output The possible values of this parameters are listed in table 5 The default value of this parameter is A 3 2 28 integer page _wvfns This controls the paging of wavefunctions to disc in order to save memory If this variable is 0 no paging will be performed If less than 0 all wavefunctions will be paged to disc If the value of this variable is greater than 0 all wavefunctions requiring more memory than this value in megabytes will be paged to disc The default value of this parameter is 0 2 29 integer rand_seed This controls the initialisation of the random number sequence If rand_seed is 0 the seed for the random number generation is selected pseudorandomly If this parameter is non zero the value is used as a seed for the random number generator The default value of this parameter is 0 2 30 character data_distribution This parameter determines the parallelisation strategy used The possible values are e Kpoint only k point parallelisation will be used e Gvector only g vector parallelisation will be used e Mixed a combination of k point and g vector parallelisation will be used e Default The optimal parallelisation strategy for the architecture will be
57. of the non local pseu dopotential projectors PSPOT_BETA_PHI_TYPE S pspot_beta_phi_type This defines the representation real or reciprocal space used for calculating the lt 6 gt overlaps Table 7 Parameter file keywords controlling exchange correlation pseudopotential and basis set Argu ment types are represented by I for a integer R for a real number P for a physical value L for a logical value D for a keyword that may simply be defined present or not and S for a text string The keywords OPT_STRATEGY and OPT_STRATEGY_BIAS may not both be defined in the same parameter file 16 Keyword Type Corresponding Description Variable Basis Set Parameters BASIS_PRECISION S basis_precision The accuracy of the basis set See Sec tion 2 36 for options CUT_OFF_ENERGY P cut_off_energy The cut off energy for the plane wave basis set GRID_SCALE R grid_scale The grid size as a multiple of the diam eter of the plane wave sphere FINE_GMAX P fine_gmax Defines the size of the fine grid FINITE_BASIS_CORR S finite_basis_corr Perform finite basis set correction when cell parameters change See Section 2 39 for options BASIS_DE_DLOGE P basis_de_dloge The derivative of total energy w r t log of basis cut off energy Only used if FINITE_BASIS_CORR MANUAL FINITE_BASIS_NPOINTS I finite_basis_npoints The number of points used to estimate the derivative of total energy w r t log of basis cut off
58. on The default value of this parameter is First 2 101 logical md_extrap_fit If md_extrap_fit TRUE the best extrapolation parameters will be calculated at each iteration Oth erwise fixed extrapolation parameters will be used The default value of this parameter is TRUE 2 102 character md_damping_scheme This controls the damping scheme used during damped MD geometry optimisation The possible values for this parameter are e Independent e Coupled e SteepestDescents The default value of this parameter is Independent 40 2 103 integer md_damping_reset Reset the damping factors after this number of iterations if convergence has not been achieved If this parameter is set to 0 the damping factors will never be reset The default value of this parameter is 30 2 104 logical md_opt_damped_delta_t If md_opt_damped_delta_t TRUE the best optimal time step will be calculated at each iteration during damped molecular dynamics Otherwise a fixed time step will be used The default value of this parameter is FALSE 2 105 real md_elec_energy tol The tolerance for accepting convergence of the total energy in an electronic minimisation during an MD run The default value for this parameter is the same as elec_energy_tol 2 106 real md_elec_eigenvalue_tol The tolerance for accepting convergence of a single eigenvalue during DIIS minimisation while performing an MD run The default value for
59. ost Unix or Linux Fortran compilers store these files in the current directory Though hidden these files do use disk space which may lead to mysterious exceeding of disk quota In many cases this location may be changed by setting the environment variable TMPDIR to another directory path The mechanism for changing temporary file directories should be documented in your compiler s manual 4 Auxilliary tools This release contains a number of programs and tools in addition to CASTEP Some of these are PERL scripts which require the Perl 5 language to be installed on your system Others are Fortran and are compiled by the command Make tools Only sketchy documentation is available at this stage 4 1 Fortran Tools charge2d Extracts a 2d slice of charge density from the seed check file for plotting See file example2d in in the New_Code Source Tools directory geom2xtl This program will convert a seedname geom output file from a CASTEP 3 02 geometry opti misation run into standard xt1 format for viewing 46 geom2xyz This program will convert a seedname geom output file from a CASTEP 3 02 geometry optimisation run into standard xtl format for viewing or animation mdxyz This program will convert a seedname md output file from a CASTEP 3 02 geometry optimisation run into standard xt1 format for viewing or animation castep2casino The CASTEP2CASINO program takes a model file from a Castep calculation and writes out a Casino forma
60. pect to the log of basis cut off energy The cut off energies at which the total energy is calculated in order to estimate the derivative will be chosen symmetrically about the chosen cut off energy for the calculation The default value of this parameter is 5 eV Only used if finite_basis_corr AUTO 2 43 logical fixed_npw Logical flag to indicate if the basis should be fixed during variable cell calculations The alternative is to allow the number of basis states to vary while fixing the cut off energy The default value of this parameter is TRUE 2 44 integer nelectrons The total number of electrons in the system If the CHARGE keyword is specified nelectrons will be chosen such that the total system charge is equal to the argument of CHARGE Alternatively if NUP and NDOWN are specified the nelectrons will be the sum of the arguments of NUP and NDOWN If the number of electrons is not specified in the parameter file the default value will be chosen such that the system is charge neutral 32 2 45 integer nup The number of spin up electrons If SPIN has been specified then nup B2te lt trons SPIN If neither NUP nor SPIN have been specified nup 2 2S 2 5 2 46 integer ndown The number of spin down electrons If SPIN has been specified then ndown Betectrons SPIN If neither NDOWN nor SPIN have been Je ndown B2 2c rons 2 47 integer nspins The number of spin components If th
61. rs specified The sum of the weights must be equal to 1 KPOINT_MP_GRID J I Ix This specifies the dimensions of the Monkhorst Pack grid requested in the directions of the reciprocal space lattice vectors KPOINT_MP_SPACING R units The single entry is the maximum distance between k points on the Monkhorst Pack grid The dimen sions of the grid will be chosen such that the maximum separation of k points is less than this units specifies the units in which the k point spacing is defined If not present the default is A7 KPOINT_MP_OFFSET R R Rk This specifies the offset of the Monkhorst Pack grid with respect to the origin of the Brillouin zone The three entries are the offset in fractional coordinates relative to the reciprocal lattice vectors The k point set for performing optical matrix element calculations can be specified in the same manner using version of the keywords above with OPTICS_ prepended The same restrictions regarding mutually exclusive keywords apply For a non self consistent band structure calculation the k points may be defined along a path through reciprocal space or a list of k points 7 BLOCK BS_KPOINT_PATH Ry Rij Riz Ro Raj R k ENDBLOCK BS_KPOINT_PATH The three numbers on each line are the fractional positions of the k point relative to the recipro cal space lattice vectors The k points define a continuous sequence of straight line segments unless the keyword BREAK appears on a separate line withi
62. run CHECKPOINT S checkpoint The model file to which model data should be written TASK S task The job to be performed CALCULATE_STRESS L calculate_stress If TRUE this forces the claculation of the stress tensor for any task RUN_TIME I run_time The maximum run time for the job If this is lt 0 no limit will be imposed NUM_BACKUP_ITER I num_backup_iter The number of geometry optimisation MD or phonon iterations between writ ing backup restart files BACKUP_INTERVAL I backup_interval The interval in seconds between back ups in geometry optimisation MD or phonon PRINT_CLOCK L print_clock Flag to indicate if timing information should be printed during the run LENGTH_UNIT S length_unit The unit of length for output MASS_UNIT S mass_unit The unit of mass for output TIME_UNIT S time_unit The unit of time for output CHARGE_UNIT S charge_unit The unit of charge for output ENERGY_UNIT S energy_unit The unit of energy for output FORCE_UNIT S force_unit The unit of force for output VELOCITY_UNIT S velocity_unit The unit of velocity for output PRESSURE_UNIT S pressure_unit The unit of pressure for output INV_LENGTH_UNIT S inv_length_unit The unit of inverse length for output FREQUENCY UNIT S frequency_unit The unit of frequency for output FORCE_CONSTANT_UNIT S force_constant_unit The unit of force constant for output VOLUME_UNIT S volume_unit The unit of volume for output Table 6 Parameter file keywords controlling general
63. s 100 2 94 real mddeltat The time step for molecular dynamics The default value of this parameter is 1 fs 2 95 character md ensemble The ensemble to use for molecular dynamics The options are NVT NVE The default value for this parameter is NVE 2 96 real md temperature The temperature for molecular dynamics The default value for this parameter is 300K 39 2 97 character md_thermostat The thermostat to use for molecular dynamics The options are Nos Hoover Langevin The default value for this parameter is Nos Hoover 2 98 real mdnoset The characteristic time for the Nos parameter when using the the Nos Hoover thermostat The Nos mass is calculated from this This parameter is unused if the Nos Hoover thermostat has not been selected The default value of this parameter is 10 x md_delta_t 2 99 real md_langevin_t The Langevin damping time when using the Langevin thermostat This parameter is unused if the Langevin thermostat has not been selected The default value of this parameter is 100 x md_delta_t 2 100 character md_extrap The extrapolation scheme to use for wavefunction and charge density if using density mixing during molecular dynamics including damped MD The options are None No extrapolation used First First order extrapolation Second Second order extrapolation Mixed Alternating first and second order extrapolati
64. t PDOS_CALCULATE_WEIGHTS L pdos_calculate_weights Calculate the band weights for a partial density of states analysis Table 11 Parameter file keywords controlling density mixing and population analysis Argument types are represented by I for a integer R for a real number L for a logical value and S for a text string 20 Keyword Type Corresponding Variable Description Geometry Optimisation Parameters GEOM_METHOD GEOM_MAX_ITER GEOM_ENERGY_TOL GEOM_FORCE_TOL GEOM_DISP_TOL GEOM_STRESS_TOL GEOM_CONVERGENCE_WIN GEOM_MODULUS_EST GEOM_FREQUENCY_EST S geom_method geom_max_iter geom_energy_tol geom_force_tol geom_disp_tol geom_stress_tol geom_convergence_win geom_modulus_est geom_frequency_test The method to use for geometry opti misation The maximum number of geometry op timisation iterations perform The convergence tolerance for the total energy per atom when finding ground state structure The convergence tolerance for the max imum force on the ions when finding the ground state ionic positions The convergence tolerance for the max imum ionic displacement in a step when finding the ground state ionic positions The convergence tolerance for the max imum stress when finding the ground state cell parameters The number of geometry optimisation iterations during which the convergence criteria must be met for convergence to be accep
65. ted An estimate of the bulk modulus of the system An estimate of the average phonon fre quency at the gamma point Table 12 Parameter file keywords controlling geometry optimisation Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string 21 Keyword Type Corresponding Variable Description Band Structure Parameters BS_MAX_ITER BS_EIGENVALUE_TOL BS_MAX_CG_STEPS BS_NEXTRA_BANDS BS_PERC_EXTRA_BANDS BS_NBANDS BS_XC_FUNCTIONAL bs_max_iter bs_eigenvalue_tol bs_max_cg_steps bs_nbands bs_xc_functional The maximum number of iterations when calculating the band structure The convergence criteria for an eigen value during a band structure calcula tion The maximum number of conjugate gradient steps in the band structure minimisation before resetting The number of extra bands above the number of valence bands at each k point when calculating the band struc ture The precentage of extra bands above the number of valence bands at each k point when calculating the band struc ture The number of bands at each k point when calculating the band structure The exchange correlation functional to use for band structure calculations Molecular Dynamics MD_NUM_ITER MD_DELTA_T MD_ENSEMBLE MD_TEMPERATURE MD_THERMOSTAT MD_NOSE_T MD_LANGEVIN_T u
66. this parameter is elec_eigenvalue_tol 2 107 integer md_elec_convergence_win The total energy or eigenvalue must lie within md_elec_energy_tol or md_elec_eigenvalue_tol re spectively for the last md_elec_convergence_win iterations for the convergence criteria to be met during an MD run The value of md_elec_convergence_win must be greater than or equal to 2 The default value of this parameter is elec_convergence_win 2 108 integer optics_nbands The number of bands at each k point when performing an optical spectrum calculation If OPTICS NBANDS is present in the parameter file the value of bs_nbands is determined by this keyword If OPTICS_NEXTRA_BANDS is specified optics nbands max nup ndown OPTICS_NEXTRA_ BANDS If OPTICS_ PERC_EXTRA_BANDS is specified optics nbands max nup ndown x 14 OPTICS PERC EXTRA BANDS The default value of this parameter is 3 x nbands 2 109 character len 15 optics_xc_functional This parameter determines the exchange correlation functional used for calculation of optical spectra The possible values are the same as those for bs_xc_functional The default value of this parameter is bs_xf_functional 2 110 character tssearch method The method used for transition state searches Possible values for this parameter are e LSTQST The default value of this parameter is LSTQST 41 2 111 character tssearch_lstqst_protocol The protocol used for an LST QST transition st
67. tron Volt eV E ev st Milli Electron Volt meV E mev x 107 Rydberg Ry E ry i 5 Millirydberg mRy E mry 5 x 1074 kJ mol kJ mol E kj mol ONG kcal mol kcal mol E kcal mol NOONE Joule J E j ct Erg erg E erg fata Hertz Hz E hz Megahertz MHz E mhz a x 108 Gigahertz GHz E ghz aoe x 10 Terahertz THz E thz A x 10 Wavenumber cm 1 E cm 1 ohe x 10 Kelvin K E k Sko Hartree Bohr Ha Bohr F hartree bohr 1 eV A eV A F ev ang z x 101 Newton N F n aos dyne dyne F dyne ass x 10 5 Table 4 The units of length mass time charge energy and force in which physical data may be input and output The dimensions for which unit conversion is provided are as follows L length M mass T time C charge E energy F force V velocity P pressure 1 L reciprocal length F L Force constant and Vol Volume The default for each dimension is indicated by a The relative values are given in terms of SI fundamental constants 13 Unit Abbreviation Dimension Identifier Value atomic units Atomic Unit of Velocity auv V auv 1 Angstom ps A ps V ang ps x 10 Angstom fs A fs V ang fs x 10 Bohr ps Bohr ps V bohr ps a Bohr fs Borh fs v bohr fs Se Metre Second m s V m s i Hartree Bohr Ha Bohr 3 P hartree bohr 3 1 eV Angstrom eV A 3 P ev ang 3 a x 108 Pascal Pa P pa ston Megapascal MPa P mpa zis x 10 Gigapascal GPa P gpa ales x 10 Atmosphere Atm P atm 101325020 x 106 bar b
68. tted file in seedname casino this needs to be renamed pwfn data in order for Casino to recognise it bands2dos This program will convert a jseedname bands output file from a NEWTEP bandstructure run into a DOS E x y format for plotting NB Input file gives energies in AU ie Hartrees whereas we give an output file in eV 4 2 PERL Tools dispersion pl A PERL program for plotting phonon dispersions or band structures Requires perl 5 005 or newer and xmgrace In basic use dispersion pl reads the phonon frequencies from a seedname castep or seedname phonon file and prints out a table If the option xg is also given and the xmgrace graph potting program is installed then the script will attempt to create a plot of the dispersion curves If the seedname phonon file is given the script also makes a best attempt to determine where bands cross based on the eigenvectors read from the file This may be tuned using the ftol option which gives the maximum Af considered when searching for branches to join The script can also read in a file of experimental data points and overplot these Each line must contain 3 numbers specifying the g point and one or more frequency data Ma Hb Ge fu fa Qa q4 Qe fa fz If the file contains a blank line the data following is considered to belong to a separate dataset and will be plotted using a distinct symbol Alternatively it can plot bandstructures from a seedname castep or seedname bands fi
69. umerically approximate the dynamical matrix N B This can only be used for qpoint 0 0 0 e LINEARRESPONSE Linear response will be used to calculate the dynamical matrix This can be applied for arbitraty qpoint The alias DFPT is accepted for LINEARRESPONSE for the value of the PHONON_METHOD key word The parameter value will be set to LINEARRESPONSE in this case The default value of this parameter is LINEARRESPONSE 2 123 real kind dp phonon_dos_spacing The resolution of the density of states calculation for phonons The default value of this parameter is 10 cm71 2 124 real kind dp phonon_finite_disp The amplitude of the ion perturbation used in a finite displacement phonon calculation The default for this parameter is 0 01 atomic units 2 125 logical phonon_calc_lo_to_splitting Flag to select whether to compute non analytic contribution to dynamical matrix from long ranged elec tric field effects responsible for LO TO splitting This requires calculation of the dielectric permittivity by efield linear response and the Born effective charges The default value of this parameter is TRUE 43 2 126 logical phonon_sum_rule Selects whether to explicitly correct the dynamical matrix to enforce the acoustic q 0 phonon sum rule i e that 3 modes have zero frequency at q 0 The default value of this parameter is FALSE 2 127 logical calculate_born_charges Selects whether to compute Born
70. vu H e md_num_iter md_delta_t md_ensemble md_temperature md_thermostat md_nose_t md_langevin_t The number of MD time steps The time step for molecular dynamics The ensemble for the molecular dynam ics run The temperature for the molecular dy namics run The thermostat for the molecular dy namics run The value for the characteristic Nos Hoover time Only used if Nos Hoover thermostat has been chosen The damping time for the Langevin thermostat Only used if the Langevin thermostat has been chosen Table 13 Parameter file keywords controlling band structure and molecular dynamics Argument types are represented by I for a integer R for a real number P for a physical value L for a logical value and S for a text string Only one of BS NBANDS BS_NEXTRA_BANDS and BS_PERC_EXTRA_BANDS may be present in a parameter file 22 Keyword Type Corresponding Description Variable Molecular Dynamics Continued MD_EXTRAP S md_extrap The extrapolation scheme to use for molecular dynamics MD_EXTRAP_FIT L md_extrap_fit Use best fit extrapolation parameters MD_ DAMPING_SCHEME S md_damping_scheme Controls the scheme used for damped MD geometry opti misation MD_DAMPING_RESET I md_damping_reset Reset the damping factors after this number of itera tions if convergence has not been achieved MD_OPT_DAMPED_DELTA_T L md_opt_damped_delta_t Use optimised time step for damped molecular dynam
71. y specification of pseudopotentials CASTEP 4 2 read its pseudopotentials from a single large file which was the concatenation of the individual files for all of the elements In contrast CASTEP 3 02 requires that the pseudpotental file are specified by name in a block species_pot in the cel1 file A comprehensive selection of pseudopoten tial files is supplied in the database References 1 R Car and M Parrinello Unified approach for molecular dynamics and density functional theory Phys Rev Lett 55 1985 no 22 2471 2474 2 Lyndon J Clarke Ivan Stich and Mike C Payne Large scale ab initio total energy calculations on parallel computers Comp Phys Commun 72 1992 no 4 14 28 3 X Gonze and C Lee Dynamical matrices born effective charges dielectric permittivity tensors and interatomic force constants from density functional perturbation theory Phys Review B 55 1997 10355 10368 48 4 K Laasonen R Car C Lee and D Vanderbilt Implementation of ultrasoft pseudopotentials in abinitio molecular dynamics Phys Review B 43 1991 6796 6799 5 Richard M Martin Electronic structure Basic theory and methods Cambridge 2004 ISBN 0521782856 6 M C Payne M P Teter D C Allen T A Arias and J D Joannopoulos Iterative minimization techniques for ab initio total energy calculations molecular dynamics and conjugate gradients Rev Mod Phys 64 1992 no 4 1045 1097 7 M

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