The workflow transferring from VASP to CASTEP is quite similar. Within VASP, there are four main files that you need for a calculation:
- POSCAR – gives the positions of the atoms within the unit cell and its lattice vectors.
- KPOINTS – sets the k-point mesh to be used.
- POTCAR – determines the type of pseudopotential to be used.
- INCAR – controls most of the main calculation parameters.
On the other hand, within CASTEP, there are two files, the seed.cell and the seed.param files, where seed is an arbitrary name you give to the system. The seed.cell essentially contains all of the POSCAR and KPOINT parameters at once. In CASTEP, the pseudopotential is automatically generated by the programme, so you do not need to procure a POTCAR file of any sort. The specific pseudopotential which you would like to use (i.e. NCP or USP) can be set within seed.cell file as well. The seed.param file is essentially the equivalent to the INCAR file in VASP and it controls the same types of calculation parameters (e.g. cutoff, XC functional, etc.).
ASE supports CASTEP input and output formats, so atomic models can be written out into a seed.cell file the same way a POSCAR is written out with
ase.io.write using the keyword
format=castep-cell. Additionally, if you are already using the VASP calculator (
ase.calculators.vasp) within ASE to prepare your input parameters/files, there is also one for CASTEP (
ase.calculators.castep) as well.