Preparing a POTCAR: Difference between revisions

Revision as of 07:58, 11 June 2024

The POTCAR is an input file that holds the pseudopotential for each element in the structure. The templates for each element can be downloaded from the VASP Portal. Copy the template to one file in the execution directory in the same order as the elements are specified in the POSCAR, e.g., by entering

 cat ~/potpaw_PBE.64/C/POTCAR ~/potpaw_PBE.64/O_h/POTCAR > POTCAR

As explained in detail below, there are sometimes multiple templates for one element with subtle differences.

Tip: Generally opt for the standard, computationally cheapest POTCAR files, but test if the property of interest is sensitive to the choice of the pseudopotential.

Step-by-step instructions

Step 1: Select a POTCAR for a certain family of exchange-correlation (XC) functionals and version.

Tip: Amongst all available potentials, the standard choice is to use the latest GGA version based on LEXCH=PE.

All potentials are constructed based on solving the scalar relativistic Schrödinger equation for a reference system with a certain XC functional. 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. We recommend using the latest available potentials. Older versions are available to ensure reproducibility.

Step 2: Choose a POTCAR with a different atomic configuration, hard or GW variant.

Tip: The standard choice is to use the plain version without suffixes.

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.

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 must be concatenated. The order of files must correspond to the order of the 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! You can copy the POTCAR to the working directory if you have only one element in your structure.

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 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 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 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.

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

Related tags and sections

Category:Pseudopotentials, POTCAR, Choosing pseudopotentials, Theory:Pseudopotential basics, Projector-augmented-wave formalism, Available pseudopotentials

@@ Line 1: / Line 1: @@
-The {{FILE|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 [https://www.vasp.at/sign_in/portal/ VASP Portal].
+The {{FILE|POTCAR}} is an [[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 template to one file in the execution directory in the same order as the elements are specified in the {{FILE|POSCAR}}, e.g., by entering
+  cat ~/potpaw_PBE.64/C/POTCAR ~/potpaw_PBE.64/O_h/POTCAR > POTCAR
+As explained in detail below, there are sometimes multiple templates for one element with subtle differences.
+{{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 1:''' Select a POTCAR family.
+'''Step 1:''' Select a {{FILE|POTCAR}} for a certain family of [[Exchange-correlation functionals|exchange-correlation (XC) functionals]] and version.
+{{NB|tip|Amongst all [[Available PAW potentials|available potentials]], the standard choice is to use the latest GGA version based on {{TAG|LEXCH}}{{=}}PE.|:}}
-: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.
+: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.
-'''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 2:''' Choose a {{FILE|POTCAR}} with a different atomic configuration, hard or GW variant.
+{{NB|tip|The standard choice is to use the plain version without suffixes.|:}}
+: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]].
 '''Step 3:''' Combine the potentials.
-:VASP expects a single POTCAR file in the working directory, containing all species present in the structure. The {{FILE|POTCAR}} files can just be concatenated together. The order of files must correspond to the order of 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}}! If you have only one element in your structure, you can just copy the {{FILE|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.
 ==Recommendations and advice==
 {{NB|mind| Mismatched order of species in the {{FILE|POSCAR}} and {{FILE|POTCAR}} files is a common mistake! Add species names to your {{FILE|POSCAR}} to receive a warning if this happens.}}
-{{NB|mind|You can mix and match {{FILE|POTCAR}} families. Even combining pseudopotentials generated with different exchange-correlation functionals is fine within the PAW formalism. However, make sure that you set the {{TAG|GGA}} tag in the {{FILE|INCAR}}.}}
+{{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 POTCAR for the Heusler alloy TiCo<math>_2</math>Si==
+==Example for preparing a {{FILE|POTCAR}} for the Heusler alloy TiCo<math>_2</math>Si==
-In this example we want to prepare a 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<math>_2</math>Si. We are interested in the size of the magnetic moments.
 The structure is defined by the following {{FILE|POSCAR}}:
@@ Line 38: / Line 44: @@
 .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_sv 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.
+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.
-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
 ==Related tags and sections==
-[[:Category:Pseudopotentials]], [[POTCAR]], [[Choosing pseudopotentials]], [[:Theory:Pseudopotential basics]], [[Projector-augmented-wave formalism]], [[Available pseudopotentials]], [[Recommended PAW potentials for calculations of mainly occupied states]], [[Recommended PAW potentials for calculations involving unoccupied states]]
+[[:Category:Pseudopotentials]], [[POTCAR]], [[Choosing pseudopotentials]], [[:Theory:Pseudopotential basics]], [[Projector-augmented-wave formalism]], [[Available pseudopotentials]]