Pseudopotentials

The general format for entering the pseudo potentials in the input file is:

• The input for a new atom type is started with a ``*'' in the first column. This line further contains:
  • the file name (ECPNAME) where to find the pseudopotential information starting in column 2
  • and several labels:

    .

    The first label
    [GAUSS-HERMITE, KLEINMAN-BYLANDER]
    specifies the method to be used for the calculation of the nonlocal parts of the pseudopotential (see sections 7.14.1 and 7.14.2 for some details). It can be omitted for Vanderbilt pseudopotentials and Goedecker-Teter-Hutter pseudopotentials. For semi-local pseudopotentials the default is Gauss-Hermite integration with 20 special points. The number of integration points can be changed using GAUSS-HERMITE=xx.

    .

    It is further possible to specify nonlinear core correction [NLCC] and the width of the ionic charge distribution [RAGGIO]. (Default is no NLCC and the default value for RAGGIO is 1.2.)

    .

    The label UPF indicates that the pseudopotential was stored using the Universal Pseudopotential Format as implemented in the Quantum Espresso package. The reader in CPMD is based on an early draft of the format and not compatible to most currently available UPF format potential files.

    .

    For Vanderbilt ultrasoft pseudopotentials one of the following options has to be specified: BINARY indicates the binary version of the output file from Vanderbilt's atomic code.
    FORMATTED indicates the formatted version of the Vanderbilt pseudopotential files after a conversion with the program `reform.f' from the Vanderbilt atomic code package (see section 1.7)
    For Vanderbilt pseudopotentials the option NLCC is ignored. The nonlinear core correction will always be used if the pseudopotential was generated with a partial core and that information is directly encoded into the pseudopotential file.
    It is strongly recommended to use only Vanderbilt pseudopotentials that were generated with a new version of Vanderbilt's atomic code (version 7.3.0 or newer).

    .

    The label CLASSIC indicates that the following atoms are to be treated with classical force fields only. See section &CLASSIC for more information.

    .

    The label _EAM_ indicates that the following atoms are treated using the EAM approach.

    .

    The label FRAC indicates that the core charge of a pseudopotential should not be rounded to the closest integer for the calculation of the number of electrons (for pseudopotentials with fractional core charge).

    .

    The label ADD_H indicates that the potential should used to saturate dangling bonds or ``hydrogenize'' united atom potentials in a CPMD/Gromos-QM/MM calculation (see section 9.16 for more details).

• The next line contains information on the nonlocality of the pseudopotential (LMAX, LOC, SKIP).
• On the following lines the coordinates for this atomic species have to be given.
  The first line gives the number of atoms (natoms) of the current type.
  Then the coordinates of the atoms are given (by default in Cartesian coordinates). For CPMD/Gromos-QM/MM calculation, however, the Gromos atom numbers have to be given instead of coordinates (see section 9.16 for more details).

The information on the nonlocal part of the pseudopotential can be given in two different styles:

-

You can specify the maximum $l$ - quantum number with ``LMAX=$l$ '' where $l$ is S, P or D.
If this is the only input, the program assumes that LMAX is the local potential (LOC).
You can use another local function by specifying ``LOC=$l$ ''.
In addition it is possible to assign the local potential to a further potential with ``SKIP=$l$ ''.

-

Alternatively you can specify these three angular quantum numbers by their numerical values (S=0, P=1, D=2) in the order ``LMAX LOC SKIP''.
If values for LOC and SKIP are provided outside the range 0 - LMAX the program uses the default.

Examples: The following lines are equivalent

LMAX=P

LMAX=P LOC=P

1 1 2

1 2 2

Note: Also for Vanderbilt and Goedecker pseudopotentials this line has to be using a correct syntax, but the actual values are ignored. The equivalent information is taken directly from the pseudopotential files instead.