Overview

CASTEP has a built-in library of pseudopotentials which is usually updated each release. We refer to CASTEP's build-in pseudopotentials as on-the-fly generated (or OTFG). The default OTFG pseudopotentials are accurate ultrasoft pseudopotentials. These are used if species_pot block is not defined in the cell file - or an empty block is given

%block species_pot
%endblock species_pot

For preliminary investigations and high-throughput calculations you might want to choose the QC5 set of ultrasoftpotentials which are faster, but slightly less accurate than the default set. These are designed to give converged results at 500eV for all elements:

%block species_pot
QC5
%endblock species_pot

For properties that require norm-conserving pseudopotentials, you can select CASTEP's latest OTFG norm-conserving set with the following in the in your .cell file.

%block species_pot
NCP
%endblock species_pot

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 ultrasoft 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

A complete list of the availible OTFG definitions follows:

String	Description
NCP	Alias for the most recent set of norm conserving potentials
QC5	High through put set (delta=1.7meV, 0.8meV excluding N,O,Cr,Mn)
HARD	"Ultimate" set of HARD pseudopotentials
C7	USP definitions as of CASTEP 7.0 (C7)
C8	USP definitions as of CASTEP 8.0 (C8)
C9	USP definitions as of CASTEP 9.0/16.0 delta=0.5meV
NCP9	Set of Norm Conserving pseudopotentials CASTEP 9.0/16.0 (NCP9)(delta=1.1meV)
C17	USP definitions, CASTEP 17.0 (C17)
NCP19	Set of Norm Conserving pseudopotentials CASTEP 17.0 (NCP17)
C18	USP definitions, CASTEP 18.0 (C18)
NCP18	Norm Conserving pseudopotentials CASTEP 18.0 (NCP18)
C19	USP definitions, CASTEP 19.0 (C19) delta=0.442 meV
NCP19	Norm Conserving pseudopotentials CASTEP 19.0 (NCP19) delta=1.098 meV

Pseudopotential files

CASTEP can also read in pseudopotentials from files

Format	Origin
.usp	as generated by CASTEP (note both USP and NCP use this format)
.uspso	as generated by CASTEP, with spin-orbit coupling
.recpot	as generated by OPIUM (also legacy CASTEP files)
.UPF	as generated by Quantum Espresso

Note that properties using PAW augmentation will not be available when using file based pseudopotentials (OTFG is required) - this includes all NMR/EPR properties and EELS spectra.