CASTEP

CASTEP Pseudopotentials

Which pseudopotential library should I use for functionality which only works with norm-conserving pseudopotentials?

A. In general, the most accurate pseudopotentials are the latest "on-the-fly" generated ones. CASTEP will generate these automatically if you specify:

 %block species_pot
NCP
%endblock species_pot 

in your <seed>.cell file. Please note that, even though this will generate norm-conserving pseudopotentials, the filenames will still end with ".usp" because they use the ultrasoft pseudopotential file format to store the potentials.

What pseudopotential libraries are available for use with CASTEP?

A. CASTEP has a built-in library of pseudopotentials which is usually updated each release. The default pseudopotentials are accurate ultrasoft pseudopotentials, but you can choose norm-conserving instead (see above) or choose a faster, but slightly less accurate, set:

 %block species_pot
QC5
%endblock species_pot 

which is suitable for preliminary investigations and high-throughput calculations. For backwards compatibility you can also select pseudopotentials from earlier versions on the on-the-fly database, e.g. use

 %block species_pot
C17
%endblock species_pot 

to select the pseudopotentials from CASTEP version 17. You can also specify the pseudopotential on a per-element basis, e.g.

 %block species_pot
Fe  C17
 O  NCP
Ba  QC5
%endblock species_pot 

There is also an old library of pseudopotential files available, but these are not as accurate as modern pseudopotentials and are only provided for reproducing old results or for quick tests and demonstrations.