Geometry Optimisation with CASTEP

More documents

Recommendations

Info

Next: Basis Set Parameters Up: The .param file Previous: The .param file General Job Parameters An important first choice is which method to use for optimisation of the ionic positions. The default option is the Broyden-Fletcher-Goldfarb-Shannon (BFGS) method and this is used throughout the rest of this user guide. For fixed cell calculations there are two other options, damped molecular dynamics geom_method : damped_md and delocalised internal coordinates geom_method : delocalized The user is free to learn about these methods from the literature and try them out if they suit a particular problem. Since we will be doing variable cell calculations later on we will stick with BFGS. The verbosity of information in the output files is controlled by iprint : value value can be 0,1,2 or 3 in order of increasing verbosity with a default value of 1, which in most cases will be sufficient to understand how the calculation has progressed. iprint : 3 is for full debugging. For users who wish to know a little bit more about what occurs during a calculation it might be interesting to set iprint : 2. If a calculation is unexpectedly interrupted many hours of work might be lost. CASTEP automatically backs up the calculation after every 5 BFGS steps. The parameter num_backup_iter : value allows the backup interval to be user specified. For very slow jobs it is sensible to back up the results after every BFGS step num_backup_iter : 1
When a calculation that was stopped is resumed the parameter continuation : default must be included so that the calculation will read the .check file and use the last completed BFGS step as a starting point for the calculation. This feature is essential when the calculation is run on large shared computational facilities where the run time per job is restricted. It is possible to choose whether the algorithm should favour a speedier calculation at the cost of using more RAM during the calculation or whether to to slow down the calculation and make it less RAM intensive. opt_strategy : value value can be 'MEMORY' or 'SPEED'. The default is for a balance between memory usage and performance. If the calculation is at all likely to be RAM limited then MEMORY should be chosen. On RAM extensive architectures SPEED should be chosen. SPEED should also be used for most clusters, multiple processors or supercomputers because these write data temporarily to disk so as to conserve RAM which significantly hampers performance. Next: Basis Set Parameters Up: The .param file Previous: The .param file 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: Next: General Job Parameters Up: In
Page 25 and 26: Next: Electronic Minimisation Param
Page 27 and 28: Next: Example - Bulk Silicon Up: Th
Page 29 and 30: the default value is 3 but it must
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

Create successful ePaper yourself

Delete template?

Save as template?