Preparing a POTCAR

The POTCAR is a VASP input file which holds the pseudopotentials and needs to be present in the execution directory for VASP to run. Differnt pseudopotential families containing different variants of these files for the whole periodic table can be downloaded from the VASP Portal.

Step-by-step instructions

Step 1: Select a POTCAR family.

We recommend the use of the latest available potentials, currently the potpaw_LDA.64 and potpaw_PBE.64 sets. For compatibility reasons or to reproduce older calculations, it might be necessary to use another set, e.g. potpaw_LDA.54 or potpaw_GGA. All available potentials, grouped by their families, are listed in the Available_pseudopotentials section.

Step 2:: Choose a pseudopotential variant.

Depending on your system, the property you want to calculate, and the method you are using different potential variants might be optimal. This choice is often non-trivial and some testing might be required. See the Choosing pseudopotentials section.

Step 3: Combine the potentials.

VASP expects a single POTCAR file in the working directory, containing all species present in the structure. The POTCAR files can just be concatenated together. The order of files must correspond to the order of species in the POSCAR file. If species names are given in the POSCAR, and they do not match the order in the POTCAR, a warning is printed, but VASP will still run. The order given in the POTCAR will take precedence over the order in POSCAR! If you have only one element in your structure, you can just copy the POTCAR.

Recommendations and advice

Mind: Mismatched order of species in the POSCAR and POTCAR files is a common mistake! Add species names to your POSCAR to receive a warning if this happens.

Mind: You can mix and match POTCAR families. Even combining pseudopotentials generated with different exchange-correlation functionals is fine within the PAW formalism. However, make sure that you set the GGA tag in the INCAR.

Example for Preparing a POTCAR for the Heusler alloy TiCo$_2$Si

In this example we want to prepare a POTCAR for a PBE calculation of ferromagnetic TiCo$_2$Si. We are interested in the size of the magnetic moments.

The structure is defined by the following POSCAR:

TiCo2Si
 1.0
 -2.8580789844367893   -2.8580789844367889    0.0000000000000000
 -2.8580789844367889    0.0000000000000000   -2.8580789844367889
 -0.0000000000000005   -2.8580789844367889   -2.8580789844367889
Co Si Ti
 2  1  1
direct
  0.7500000000000000    0.7500000000000000    0.7500000000000000 Co
  0.2500000000000000    0.2500000000000000    0.2500000000000000 Co
  0.0000000000000000    0.0000000000000000    0.0000000000000000 Si
  0.4999999999999999    0.5000000000000000    0.5000000000000000 Ti

We will use the potpaw_PBE.64 potential set, and since we are interested in magnetic properties we should make sure to use potentials with additional semicore-states in the valence. The Co_pv and Ti_ps potentials seem appropriate for the transition metals. We do not expect Si to become magnetic and we are not interested in unoccupied states, so the Si potential seems a better choice than the harder Si_GW or even Si_sv_GW.

On a UNIX machine one can use the cat command to concatenate files together. One can redirect the output from stdout to a file using the > operator. The order in the POSCAR dictates the order in the POTCAR:

cat ~/potpaw_PBE.64/Co_pv/POTCAR ~/potpaw_PBE.64/Ti_sv/POTCAR ~/potpaw_PBE.64/Si/POTCAR > ~/scratch/TiCo2Si/POTCAR