Preparing a POTCAR: Difference between revisions

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The {{FILE|POTCAR}} file is a mandatory [[Input files|input file]] that holds the [[:Category:Pseudopotentials|pseudopotential]] for each element in the structure. The templates for each element can be downloaded from the [https://www.vasp.at/sign_in/portal/ VASP Portal]. Copy the templates to one file named {{FILE|POTCAR}} in the working directory. It is important to paste the templates in the same order as the elements are specified in the {{FILE|POSCAR}}, e.g., by entering
The {{FILE|POTCAR}} file is a mandatory [[Input files|input file]] that holds the [[:Category:Pseudopotentials|pseudopotential]] for each element in the structure. The templates for each element can be downloaded from the [https://www.vasp.at/sign_in/portal/ VASP Portal].  
There are sometimes multiple templates for one element with subtle differences.


  cat ~/potpaw_PBE.64/C/POTCAR ~/potpaw_PBE.64/O_h/POTCAR > POTCAR
==Step-by-step instructions==


As explained in detail below, there are sometimes multiple templates for one element with subtle differences.
'''Step 1:''' Select the [[Available_pseudopotentials|latest version]] of {{FILE|POTCAR}} files unless you need to use an older one to reproduce a result.
{{NB|tip|Generally opt for the standard, computationally cheapest {{FILE|POTCAR}} files, but test if the property of interest is sensitive to the choice of the pseudopotential.}}


==Step-by-step instructions==
'''Step 2:''' Choose 
* [[Available_pseudopotentials#Standard_potentials|standard potentials]] for calculations depending mainly on occupied states, e.g., within density-functional theory, using [[hybrid functionals]], or
* [[Available_pseudopotentials#GW_potentials|GW variants]] if the calculation requires high accuracy for unoccupied states, i.e., for [[optical properties|optical response]] and [[many-body perturbation theory]].


'''Step 1:''' Select a {{FILE|POTCAR}} for a certain family of [[Exchange-correlation functionals|exchange-correlation (XC) functionals]] and version.
'''Step 3:''' Select a {{FILE|POTCAR}} for a certain family of [[Exchange-correlation functionals|exchange-correlation (XC) functionals]].
{{NB|tip|Amongst all [[Available PAW potentials|available potentials]], the standard choice is to use the latest GGA version based on {{TAG|LEXCH}}{{=}}PE.|:}}
{{NB|tip|The standard choice is to use the [[Available_pseudopotentials#Standard_potentials|PBE version]] based on {{TAG|LEXCH}}{{=}}PE which has a high transferability to other [[XC functionals]].|:}}
:All potentials are constructed based on solving the scalar relativistic Schrödinger equation for a reference system with a certain [[Exchange-correlation functionals|XC functional]]. One set is available for the LDA, and one for the GGA. The transferability to other [[Exchange-correlation functionals|XC functionals]] is seamless by specifying the {{TAG|XC}} tag in the {{FILE|INCAR}}. We recommend using the latest available potentials. Older versions are available to ensure reproducibility.
:All potentials are constructed based on solving the scalar relativistic Schrödinger equation for a reference system with a certain [[Exchange-correlation functionals|XC functional]]. In most versions, one set is available for the LDA, and one for the GGA. The transferability to other [[Exchange-correlation functionals|XC functionals]] is seamless by specifying the {{TAG|XC}} tag in the {{FILE|INCAR}}.


'''Step 2:''' Choose a {{FILE|POTCAR}} with a different atomic configuration, hard or GW variant.
'''Step 4 (optional):''' Choose a [[Available pseudopotentials#Different variants specified by the suffix|different variant (reference atomic valence configuration, etc.) specified by the suffix]].  
{{NB|tip|The standard choice is to use the plain version without suffixes.|:}}
{{NB|tip|The standard choice is to use the bold version in the [[Available pseudopotentials#Recommended PAW potentials|list of PAW potentials]].|:}}
:The suffix may correspond to a harder potential necessary to describe short bond lengths or a different number of valence electrons, e.g., required to describe magnetism, as well as higher accuracy for unoccupied states required for optical response and many-body perturbation theory. See [[Choosing pseudopotentials|choosing pseudopotentials]].
:See [[choosing pseudopotentials]].
{{NB|important|Generally opt for the recommended {{FILE|POTCAR}} files, but test if the property of interest is sensitive to the choice of the pseudopotential. It may be possible to choose a computationally cheaper version or necessary to select a more demanding one.|:}}


'''Step 3:''' Combine the potentials.
'''Step 5:''' For a single element in the structure, you can copy the {{FILE|POTCAR}} to the working directory, e.g,
  cp /path/to/pot/Al/POTCAR .
:For structures with multiple elements, the selected {{FILE|POTCAR}} files must be concatenated to create one {{FILE|POTCAR}} file containing all species present in the structure. Combine the potentials by entering, for instance,
  cat /path/to/pot/Al/POTCAR /path/to/pot/C/POTCAR /path/to/pot/H/POTCAR > POTCAR


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


==Recommendations and advice==
==Recommendations and advice==
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{{NB|mind|You can mix and match {{FILE|POTCAR}} families. Even combining pseudopotentials generated with different [[XC functionals]] is possible, however make sure to specify the [[XC functional]] in the {{FILE|INCAR}}, see {{TAG|XC}}.}}
{{NB|mind|You can mix and match {{FILE|POTCAR}} families. Even combining pseudopotentials generated with different [[XC functionals]] is possible, however make sure to specify the [[XC functional]] in the {{FILE|INCAR}}, see {{TAG|XC}}.}}


==Example for preparing a {{FILE|POTCAR}} for the Heusler alloy TiCo<math>_2</math>Si==
==Example for preparing a {{FILE|POTCAR}} for the Heusler alloy TiCo<sub>2</sub>Si==


In this example, we want to prepare a {{FILE|POTCAR}} for a PBE calculation of ferromagnetic TiCo<math>_2</math>Si. We are interested in the size of the magnetic moments.
In this example, we want to prepare a {{FILE|POTCAR}} for a PBE calculation of ferromagnetic TiCo<sub>2</sub>Si. We are interested in the energy difference between the ferromagnetic and the nonmagnetic solutions.


The structure is defined by the following {{FILE|POSCAR}}:
The structure is defined by the following {{FILE|POSCAR}}:
  TiCo2Si
  TiCo2Si
   1.0
   1.0
  -2.8580789844367893   -2.8580789844367889   0.0000000000000000
  0.0000000000000000    2.8580789844367893   2.8580789844367893
  -2.8580789844367889   0.0000000000000000   -2.8580789844367889
   2.8580789844367893   0.0000000000000000   2.8580789844367893
  -0.0000000000000005  -2.8580789844367889  -2.8580789844367889
  2.8580789844367893    2.8580789844367893    0.0000000000000000
  Co Si Ti
  Co Si Ti
   2  1  1
   2  1  1
Line 42: Line 49:
   0.2500000000000000    0.2500000000000000    0.2500000000000000 Co
   0.2500000000000000    0.2500000000000000    0.2500000000000000 Co
   0.0000000000000000    0.0000000000000000    0.0000000000000000 Si
   0.0000000000000000    0.0000000000000000    0.0000000000000000 Si
   0.4999999999999999   0.5000000000000000    0.5000000000000000 Ti
   0.5000000000000000   0.5000000000000000    0.5000000000000000 Ti


We will use the potpaw_PBE.64 potential set, and since we are interested in magnetic properties, we should use potentials with additional semicore-states in the valence. The Co_pv and Ti_sv potentials seem appropriate for the transition metals. We do not expect Si to become magnetic and are not interested in unoccupied states, so the Si potential is a good choice compared to the harder, computationally more demanding Si_GW or even Si_sv_GW.
We will use the potpaw_PBE.64 potential set, and since we are interested in small energy differences caused by different magnetic solutions, we should use potentials with additional semicore-states in the valence for the 3d metals. The Co_pv and Ti_sv potentials seem appropriate for the transition metals. We do not expect Si to become magnetic and are not interested in unoccupied states, so the Si potential is a good choice compared to the harder, computationally more demanding Si_GW or even Si_sv_GW.


On a UNIX machine, one can use the <code>cat</code> command to concatenate files together. One can redirect the output from <code>stdout</code> to a file using the <code>></code> operator. The order in the {{FILE|POSCAR}} dictates the order in the {{FILE|POTCAR}}:
On a UNIX machine, one can use the <code>cat</code> command to concatenate files together. One can redirect the output from <code>stdout</code> to a file using the <code>></code> operator. The order in the {{FILE|POSCAR}} dictates the order in the {{FILE|POTCAR}}:
  cat ~/potpaw_PBE.64/Co_pv/POTCAR ~/potpaw_PBE.64/Ti_sv/POTCAR ~/potpaw_PBE.64/Si/POTCAR > ~/scratch/TiCo2Si/POTCAR
  cat ~/potpaw_PBE.64/Co_pv/POTCAR ~/potpaw_PBE.64/Si/POTCAR ~/potpaw_PBE.64/Ti_sv/POTCAR > ~/scratch/TiCo2Si/POTCAR


==Related tags and sections==
==Related tags and sections==


[[Available potentials]], {{FILE|POTCAR}}, [[Choosing pseudopotentials]], [[Theory:Pseudopotential basics]], [[Projector-augmented-wave formalism]]
[[Available potentials]], {{FILE|POTCAR}}, [[Choosing pseudopotentials]], <!--[[Theory:Pseudopotential basics]],--> [[Projector-augmented-wave formalism]]


[[Category:Pseudopotentials]][[Category:Howto]]
[[Category:Pseudopotentials]][[Category:Howto]]

Latest revision as of 13:26, 26 June 2024

The POTCAR file is a mandatory input file that holds the pseudopotential for each element in the structure. The templates for each element can be downloaded from the VASP Portal. There are sometimes multiple templates for one element with subtle differences.

Step-by-step instructions

Step 1: Select the latest version of POTCAR files unless you need to use an older one to reproduce a result.

Step 2: Choose

Step 3: Select a POTCAR for a certain family of exchange-correlation (XC) functionals.

Tip: The standard choice is to use the PBE version based on LEXCH=PE which has a high transferability to other XC functionals.
All potentials are constructed based on solving the scalar relativistic Schrödinger equation for a reference system with a certain XC functional. In most versions, one set is available for the LDA, and one for the GGA. The transferability to other XC functionals is seamless by specifying the XC tag in the INCAR.

Step 4 (optional): Choose a different variant (reference atomic valence configuration, etc.) specified by the suffix.

Tip: The standard choice is to use the bold version in the list of PAW potentials.
See choosing pseudopotentials.
Important: Generally opt for the recommended POTCAR files, but test if the property of interest is sensitive to the choice of the pseudopotential. It may be possible to choose a computationally cheaper version or necessary to select a more demanding one.

Step 5: For a single element in the structure, you can copy the POTCAR to the working directory, e.g,

 cp /path/to/pot/Al/POTCAR .
For structures with multiple elements, the selected POTCAR files must be concatenated to create one POTCAR file containing all species present in the structure. Combine the potentials by entering, for instance,
 cat /path/to/pot/Al/POTCAR /path/to/pot/C/POTCAR /path/to/pot/H/POTCAR > POTCAR 
The order of the potentials must correspond to the order of the species in the POSCAR file.
Tip: If species names are given in the POSCAR, and the order does not match the order in the POTCAR, a warning is printed, but VASP will still run.

Recommendations and advice

Important: Except for the 1st-row elements, all PAW potentials are designed to work at an energy cutoff (ENMAX tag in the POTCAR) of roughly 250 eV. This is a key aspect of making the calculation computationally cheap. We recommend performing a convergence study of the quantity of interest with respect to the energy cutoff (ENCUT tag in the INCAR).
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 XC functionals is possible, however make sure to specify the XC functional in the INCAR, see XC.

Example for preparing a POTCAR for the Heusler alloy TiCo2Si

In this example, we want to prepare a POTCAR for a PBE calculation of ferromagnetic TiCo2Si. We are interested in the energy difference between the ferromagnetic and the nonmagnetic solutions.

The structure is defined by the following POSCAR:

TiCo2Si
 1.0
  0.0000000000000000    2.8580789844367893    2.8580789844367893
  2.8580789844367893    0.0000000000000000    2.8580789844367893
  2.8580789844367893    2.8580789844367893    0.0000000000000000
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
  0.5000000000000000    0.5000000000000000    0.5000000000000000 Ti

We will use the potpaw_PBE.64 potential set, and since we are interested in small energy differences caused by different magnetic solutions, we should use potentials with additional semicore-states in the valence for the 3d metals. The Co_pv and Ti_sv potentials seem appropriate for the transition metals. We do not expect Si to become magnetic and are not interested in unoccupied states, so the Si potential is a good choice compared to the harder, computationally more demanding 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/Si/POTCAR ~/potpaw_PBE.64/Ti_sv/POTCAR > ~/scratch/TiCo2Si/POTCAR

Related tags and sections

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