Pseudopotentials

Most GPW calculations in CP2K use norm-conserving Goedecker-Teter-Hutter (GTH) pseudopotentials. A pseudopotential removes chemically inactive core electrons from the explicit electronic problem and represents their effect on the valence electrons through an effective potential. This reduces the number of electrons and avoids the very hard core density that would otherwise require extremely fine grids.

Pseudopotential files are selected in POTENTIAL_FILE_NAME, and the actual potential is selected for each atomic KIND with POTENTIAL:

&FORCE_EVAL
  &DFT
    POTENTIAL_FILE_NAME GTH_POTENTIALS
  &END DFT
  &SUBSYS
    &KIND O
      POTENTIAL GTH-PBE-q6
    &END KIND
    &KIND H
      POTENTIAL GTH-PBE-q1
    &END KIND
  &END SUBSYS
&END FORCE_EVAL

Do not confuse the POTENTIAL keyword with the identically-named POTENTIAL section that also defines a pseudopotential. Their distinction is that the keyword takes the type and name of the potential, while the section takes the complete specification and data in an internal format. Specifying only the keyword as is done above suffices for most practical usage. For those curious, CP2K will resolve user-provided inputs and compose restart files with more verbose but otherwise equivalent syntax as a new input (see MOTION/PRINT/RESTART), and such a restart file gives a glimpse of the usage of both the keyword and the section:

     &KIND "O"
       POTENTIAL "GTH-PBE-q6"
       &POTENTIAL
         2 4
           2.4455430000000000E-001 2 -1.6667214800000000E+001  2.4873113199999999E+000
         2
           2.2095592000000000E-001 1  1.8337458110000000E+001
           2.1133246999999999E-001 0
         # Potential name: GTH-PBE-Q6 for element symbol: O
         # Potential read from the potential filename: GTH_POTENTIALS
       &END POTENTIAL
     &END KIND
     &KIND "H"
       POTENTIAL "GTH-PBE-q1"
       &POTENTIAL
         1
           2.0000000000000001E-001 2 -4.1789004399999996E+000  7.2446330999999997E-001
         0
         # Potential name: GTH-PBE-Q1 for element symbol: H
         # Potential read from the potential filename: GTH_POTENTIALS
       &END POTENTIAL
     &END KIND

The suffix q6 in GTH-PBE-q6, for example, means that six valence electrons are treated explicitly. The chosen basis set should match this valence configuration; for oxygen, the common basis sets with the same suffix in the full name like DZVP-MOLOPT-GTH-q6 can be used. If some pseudopotentials without corresponding basis sets, or vice versa, are spotted in the built-in data files, consult developers for help.

Choosing a Pseudopotential

Use a pseudopotential generated for the exchange-correlation functional family used in the calculation. For example, GTH-PBE-q6 is a natural choice for PBE calculations with oxygen. Mixing functional families can be acceptable for exploratory work in some cases, but it is not a systematic route to high accuracy.

The CP2K data directory contains several pseudopotential libraries:

  • GTH_POTENTIALS contains widely used GTH potentials for common GPW calculations.

  • POTENTIAL_UZH contains the UZH protocol GTH potentials designed to be used with matching UZH basis sets.

  • NLCC_POTENTIALS and GTH_SOC_POTENTIALS contain more specialized potentials.

  • ECP_POTENTIALS contains effective core potentials for Gaussian integral based calculations.

For new GPW production inputs, prefer a matching UZH protocol pair from POTENTIAL_UZH and BASIS_MOLOPT_UZH when it is available for the element and functional family. The older GTH_POTENTIALS library remains important for reproducing established calculations and for cases where a matching UZH setup is not available.

For all-electron calculations, use POTENTIAL ALL together with an all-electron basis set and the GAPW method:

&KIND O
  BASIS_SET SVP-MOLOPT-GGA-ae
  POTENTIAL ALL
&END KIND

Consistency Checks

Useful checks when setting up a calculation are:

  • The basis set and pseudopotential should be available in the files named in the DFT section.

  • The pseudopotential valence charge should match the basis set suffix where such a suffix is used.

  • The exchange-correlation functional should be consistent with the pseudopotential family.

  • For heavy elements, decide whether a large-core, medium-core, small-core, or all-electron description is appropriate for the property of interest.

For a tested minimal GPW input using GTH pseudopotentials, see Run a First Calculation.

See Also