Geometry Optimisation with CASTEP

We must now choose a supercell to enclose as few atoms as possible but still reproduce the whole
structure. The following configuration can be used provided we include the relevant symmetry operations
in the cell file.
Figure 2:The primitive cell which we will take as our supercell
The complete .cell file for this supercell is included in the link.
The first thing that we notice is that we are using the abc format to specify the size and shape of the
lattice. The shape of our unit cell naturally suggests that we do this.
The lengths of a,b and c are the same as those in the bulk lattice. Later we will do a variable cell
calculation as both an example of how to set one up and to check how accurately the primitive cell shape
and contents can be optimised.
Note that we are using a 2x2x2 Monkhurst-Pack grid and also the inclusion of symmetry_generate
to ensure that castep is aware of the symmetry operations that our supercell satisfies.
The parameters file si.param is here
Notice that we can include the parameter line
Comment : value
This will appear in the output as a title (see the next section).
Having set up our input files we can now run the job. The job is small and we will execute it on a desktop