Geometry Optimisation with CASTEP

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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