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The {{FILE|POTCAR}} file essentially contains the pseudopotential for each atomic species used in the calculation. If the number of species is larger than one, one simply concatenates the {{FILE|POTCAR}} files of the species. On a UNIX machine you might type the line
The {{FILE|POTCAR}} file is a mandatory [[input file]]. It contains the [[pseudopotential]] for each atomic species used in the calculation.


cat ~/pot/Al/POTCAR ~/pot/C/POTCAR ~/pot/H/POTCAR > POTCAR
Simple instructions to set up a {{FILE|POTCAR}} file with the correct format: [[Prepare a POTCAR]].


to concatenate three {{FILE|POTCAR}} files. The first file will correspond to the first species in the {{FILE|POSCAR}} and the {{FILE|INCAR}} file etc.
Guide on checking which pseudopotential flavor is appropriate for a specific calculation:  [[Choosing pseudopotentials]].
{{NB|mind| It is a frequent error to give the wrong ordering in the {{FILE|POTCAR}} file!}}
{{NB|important| The settings in the {{FILE|POTCAR}} file are read-only and must not be edited.}}
No standard usage of VASP requires modifying the {{FILE|POTCAR}} file. Specifically, do not modify the {{TAG|LEXCH}} tag in the {{FILE|POTCAR}} file. If you want to select a different functional, set the {{TAG|XC}}, {{TAG|GGA}} or {{TAG|METAGGA}} tag in the {{FILE|INCAR}} file.


For VASP version ≥ 3.2, the {{FILE|POTCAR}} file also contains 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. If tags for the mass and valence exist in the {{FILE|INCAR}} file, they are checked against the parameters found in the {{FILE|POTCAR}} file, and error messages are printed. The  {{FILE|POTCAR}} files also contain a default energy cutoff ([[ENMAX]] and [[ENMIN]]); therefore, it is no longer necessary to specify {{TAG|ENCUT}} in the {{FILE|INCAR}} file. The value in the {{FILE|INCAR}} file overwrites the default in the {{FILE|POTCAR}} file. For {{FILE|POTCAR}} files with more than one species, the maximum cutoffs ([[ENMAX]] or [[ENMIN]]) are used for the calculation.
==File Format==
{{NB| important | The {{FILE|POTCAR}} file is meant to be used as read-only by the user. There is no standard usage of VASP that requires modifying the POTCAR file. Specifically do not modify the LEXCH tag in the POTCAR file: VASP recalculates the exchange-correlation energy inside the PAW sphere using the functional specified in the INCAR file and corrects the atomic energies. For this to work properly, the original LEXCH tag must not be modified in the POTCAR file.}}


To decide which potentials to use in your calculations visit our list of [[available PAW potentials]]
{{FILE|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 {{TAG|POMASS}}, their number of valence electrons {{TAG|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) {{FILE|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 {{FILE|POTCAR}} files, but required for [[METAGGA#POTCAR_files:_required_information|METAGGA calculations]]


[[Category:Files]][[Category:Input files]]
All {{FILE|POTCAR}}s end with the line <code> End of Dataset</code>.
 
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.
{{NB|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 {{FILE|POTCAR}} file itself.}}
 
; {{TAG|TITLE}}
: The first line in any {{FILE|POTCAR}} file is the title of the pseudopotential. It is later printed again under the {{TAG|TITLE}} tag. Depending on the potential set, this might be more or less verbose. In our example we have a [[Projector-augmented-wave_formalism|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.
:<code>TITEL  = PAW_PBE Ti_pv 07Sep2000</code>
{{NB|tip|You may choose this string to indicate what pseudopotential you have used in your publication to ensure the reproducibility of your results.|:}}
; {{TAG|LEXCH}}
: This tag specifies the [[exchange-correlation functional]] used to create the potential. Even if another functional is selected in the {{FILE|INCAR}} via the {{TAG|XC}}, {{TAG|GGA}} or {{TAG|METAGGA}} tag, this information is required to recalculate the exchange-correlation energy inside the PAW spheres. Here, PE stands for the PBE functional.
:<code>LEXCH  = PE</code>
; {{TAG|ZVAL}}
: This specifies the number of valence electrons considered in the pseudopotential. It is printed in the second line of the {{FILE|POTCAR}} and again in the same line as {{TAG|POMASS}}.
; {{TAG|POMASS}}
: The atomic mass in atomic units. One can increase this in [[MD|molecular dynamics calculations]] for light elements
:<code>POMASS =  47.880; ZVAL  =  10.000    mass and valenz</code>
; {{TAG|ENMAX}} and {{TAG|ENMIN}}
: These two tags are default plane-wave cutoffs for the pseudopotential in electron Volt (eV). {{TAG|ENMIN}} is the minimum viable, end {{TAG|ENMAX}} the recommended cutoff. For {{FILE|POTCAR}} files with more than one species, the maximum cutoffs ({{TAG|ENMAX}} or {{TAG|ENMIN}}) are used for the calculation. Note that the {{FILE|INCAR}} tag {{TAG|ENCUT}} overwrites the default from the {{FILE|POTCAR}}.
:<code>ENMAX  =  222.335; ENMIN  =  166.751 eV</code>
{{NB|tip|We recommend setting the {{TAG|ENCUT}} tag in the {{FILE|INCAR}} file.|:}}
; {{TAG|EAUG}}
: The energy cutoff for the plane-wave representation for the augmentation charges in eV. This might be overwritten in the {{FILE|INCAR}} using the tag {{TAG|ENAUG}}.
:<code>EAUG  =  482.848</code>
; Atomic configuration
: This block describes the atomic reference configuration used to create the pseudopotential. The first three columns, <i>n</i>, <i>l</i>, and <i>j</i> represent the principal, angular momentum, and total angular momentum <i>j</i>=|<i>l</i>+<i>s</i>| 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 ({{TAG|ZVAL}}): Add occupied states from the bottom of the table until it counts {{TAG|ZVAL}}, i.e., 10 in our example. Thus, we arrive at 3<i>p</i><sup>6</sup>3<i>d</i><sup>3</sup>4<i>s</i><sup>1</sup> for Ti_pv.
<nowiki>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</nowiki>
 
==Related tags and sections==
 
[[Available potentials]], [[Prepare a POTCAR]], [[Choosing pseudopotentials]], [[Projector-augmented-wave formalism]]
 
==References==
 
[[Category:Files]][[Category:Input files]][[Category:Pseudopotentials]]

Revision as of 10:32, 11 June 2024

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

References