Geometry Optimisation with CASTEP

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depend on the nature of the system and the method used to treat any metallic species in the system metals_method : value For insulators no special treatment is required. Including a parameter fix_occupancy : true defines the system as an insulator and metals method will be set to a default value of NONE. If the user defines fix_occupancy : false then by default a choice will be made by CASTEP for metals_method : EDFT Now with Ensemble Density Functional Theory (EDFT) the calculation is more likely to converge than with the alternative method Density Mixing (DM) and will usually require fewer SCF cycles to minimise the electronic structure for a given ionic structure. However, DM is much faster per SCF cycle than EDFT. For systems containing metallic atoms it is advisable to first try DM with max_scf_cycles : 50 and if this is failing to converge switch to EDFT. The electronic minimisation is considered to have converged when the change in the total energy from one iteration to the next remains below some tolerance value per atom for a few scf steps. The default value of the parameter elec_energy_tol : value is eV per atom and is usually suitable but it might be suitable to reduce the strictness of this tolerance limit if a calculation is consistently failing to converge. The number of iterations for which the change in the total energy must remain below elec_energy_tol is the convergence window and it can be specified by. elec_convergence_win
the default value is 3 but it must be at least 2. Next: Example - Bulk Silicon Up: The .param file Previous: Variable Cell Calculations 2005-04-04
Page 1 and 2: Next: Recipe Geometry Optimisation
Page 3 and 4: Next: Inputs Up: Geometry Optimisat
Page 5 and 6: Next: The Size and Shape Up: Inputs
Page 7 and 8: In both cases if [units] are not sp
Page 9 and 10: After the atomic symbol or the atom
Page 11 and 12: KPOINTS_MP_SPACING [units] Where is
Page 13 and 14: 2005-04-04
Page 15 and 16: Next: Atomic masses Up: The .cell f
Page 17 and 18: It is possible to fix the positions
Page 19 and 20: Next: External pressure that is Up:
Page 21 and 22: Next: General Job Parameters Up: In
Page 23 and 24: When a calculation that was stopped
Page 25 and 26: Next: Electronic Minimisation Param
Page 27: Next: Example - Bulk Silicon Up: Th
Page 31 and 32: We must now choose a supercell to e
Page 33 and 34: Next: The .castep file Up: Geometry
Page 35 and 36: 4 -2.14844155E+002 -9.84322032E-003
Page 37 and 38: BFGS: Final Configuration: ========
Page 39 and 40: Next: Other output files Up: Output
Page 41 and 42: Next: A Variable Cell calculation U
Page 43 and 44: arbitrary set of basis set paramete
Page 45 and 46: 3 -2.16474423E+002 2.10512829E-007
Page 47 and 48: Figure 6:A finite vacuum gap may ca
Page 49 and 50: 0.0000000000 0.0000000000 24.503725
Page 51 and 52: thickness We can see that the total
Page 53 and 54: It is interesting to look at the ev
Page 55 and 56: Next: About this document ... Up: G

Geometry Optimisation with CASTEP

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