POTCAR

The POTCAR file is a mandatory input file. It contains the pseudopotential for each atomic species used in the calculation.

Simple instructions to set up a POTCAR file with the correct format: Prepare a POTCAR.

Guide on checking which pseudopotential flavor is appropriate for a specific calculation: Choosing pseudopotentials.

Important: The settings in the POTCAR file are read-only and must not be edited.

No standard usage of VASP requires modifying the POTCAR file. Specifically, do not modify the LEXCH tag in the POTCAR file. If you want to select a different functional, set the XC, GGA or METAGGA tag in the INCAR file.

File Format

POTCAR files contain a header section with some tags, and large blocks of tabulated data containing the actual pseudopotential. More recent potential sets contain more information in the headers, so not all tags described below are present in all files ever distributed. Information about the atoms, i.e., their mass POMASS, their number of valence electrons ZVAL, the energy of the reference configuration for which the pseudopotential was created, etc. is present since VASP version 3.2. Since the release of the potpaw.54 potential set (VASP version 5.4) POTCAR files also contain a copyright notice and a unique hash that can be used for verification of the file.

Some data, e.g., additional information about the kinetic-energy density of the core-electrons, is not available in all POTCAR files, but required for METAGGA calculations

All POTCARs end with the line End of Dataset.

The Ti_pv potential from the potpaw_PBE.64 set, where the 3p states are included in the valence, serves as an example to explain some tags in the following.

Mind: The information below is not complete. However, we believe that it covers the most information required in practice. Some other tags are also documented in the POTCAR file itself.

TITLE

The first line in any POTCAR file is the title of the pseudopotential. It is later printed again under the TITLE tag. Depending on the potential set, this might be more or less verbose. In our example we have a PAW potential of Ti created with the PBE functional. The "_pv" suffix indicates that semicore p-states are included as valence electrons. We also see that this potential was created in September of 2000.

TITEL = PAW_PBE Ti_pv 07Sep2000

Tip: You may choose this string to indicate what pseudopotential you have used in your publication to ensure the reproducibility of your results.

LEXCH

This tag specifies the exchange-correlation functional used to create the potential. Even if another functional is selected in the INCAR via the XC, GGA or METAGGA tag, this information is required to recalculate the exchange-correlation energy inside the PAW spheres. Here, PE stands for the PBE functional.

LEXCH = PE

ZVAL

This specifies the number of valence electrons considered in the pseudopotential. It is printed in the second line of the POTCAR and again in the same line as POMASS.

POMASS

The atomic mass in atomic units. One can increase this in molecular dynamics calculations for light elements

POMASS = 47.880; ZVAL = 10.000 mass and valenz

ENMAX and ENMIN

These two tags are default plane-wave cutoffs for the pseudopotential in electron Volt (eV). ENMIN is the minimum viable, end ENMAX the recommended cutoff. For POTCAR files with more than one species, the maximum cutoffs (ENMAX or ENMIN) are used for the calculation. Note that the INCAR tag ENCUT overwrites the default from the POTCAR.

ENMAX = 222.335; ENMIN = 166.751 eV

Tip: We recommend setting the ENCUT tag in the INCAR file.

EAUG

The energy cutoff for the plane-wave representation for the augmentation charges in eV. This might be overwritten in the INCAR using the tag ENAUG.

EAUG = 482.848

Atomic configuration

This block describes the atomic reference configuration used to create the pseudopotential. The first three columns, n, l, and j represent the principal, angular momentum, and total angular momentum j=|l+s| quantum numbers. This is followed by the total energy and the occupation numbers of the orbitals. Note that fractional occupations are possible because the reference configuration does not have to be the ground state. It is possible to deduce the valence-electron configuration of the potentential using the valence electron number (ZVAL): Add occupied states from the bottom of the table until it counts ZVAL, i.e., 10 in our example. Thus, we arrive at 3p⁶3d³4s¹ for Ti_pv.

Atomic configuration
    8 entries
     n  l   j            E        occ.
     1  0  0.50     -4865.3608   2.0000
     2  0  0.50      -533.1368   2.0000
     2  1  1.50      -440.5031   6.0000
     3  0  0.50       -59.3186   2.0000
     3  1  1.50       -35.7012   6.0000
     3  2  2.50        -1.9157   3.0000
     4  0  0.50        -3.7291   1.0000
     4  3  2.50        -1.3606   0.0000

Related tags and sections

Available potentials, Prepare a POTCAR, Choosing pseudopotentials, Projector-augmented-wave formalism