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 Available_PAW_potentials.

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 Construction:Choosing_a_pseudopotential_variant.

Step 3: Combine the potentials.

VASP expects a single POTCAR file in the working directory, containing all species present in the structure. To combine e.g. potentials for titanium (with the 3p states in the valence), carbon, and hydrogen, all in the "pot" family, on a UNIX machine, you might type the line:

cat ~/pot/Ti_pv/POTCAR ~/pot/C/POTCAR ~/pot/H/POTCAR > ~/your/working/dir/POTCAR

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.