The potential keyword

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Purpose

  • This keyword is used to specify one potential for the system. It may be used multiple times (currently up to 10 times) to define multiple potentials for the system. All potentials (two- and many-body) are defined using this keyword.

Grammar

  • This keyword has multiple parameters. The format of the keyword expression is:
 potential path_to_potential [list_of_types_or_groups]
where the path_to_potential gives the path to the potential file to be used, and the list_of_types_or_groups gives the list of atom types (or groups if selected in the potential_definition that will participate in the potential. The listed types (or groups) must always be in ascending order. For many-body potentials, the list must also be sequential. For a specific many-body potential, the atoms in the xyz.in file must also be in the same order and be contiguously listed as the type/group sequence listed in the potential command (i.e. a many-body potential uses atom types 0, 1, then atoms of type 0 must be listed first in the xyz.in file and all atoms of type 1 must be listed directly after type 0). For two-body potentials, the list of numbers must still be ascending, but need not be sequential (e.g. 0 2 3 4 is acceptable). Finally, the order in which the potential keywords are used is not important. An illustration of this can be seen in the example below.

Examples

Example 1

For an MoS2/SiO2 system interacting with a Lennard-Jones potential, an example run.in file may look like:

potential_definition type
potential /path/to/GPUMD/potentials/rebo/MoS_Liang_2009.txt 2 3
potential /path/to/GPUMD/potentials/tersoff/SiO_Munetoh_2007.txt 0 1
potential /path/to/GPUMD/potential/custom/ljparams.txt 0 1 2 3
velocity 300
run 10000

By writing this, one has to make sure that the files MoS_Liang_2009.txt, SiO_Munetoh_2007.txt, and ljparams.txt have been prepared in those locations. Additionally, note that the potential for atom types 2 and 3 are defined before atom types 0 and 1. This is a legal operation as the order of potential keywords in the run.in file does not matter, though the order of the atom types in the xyz.in file does.

Caveats

  • There are a few rules that are enforced for this keyword:
  1. An arbitrary number of potentials may be defined (up to 10).
  2. Up to one many-body potential may be defined for each atom.
  3. An arbitrary number of two-body potentials may be defined for each atom.
  4. Each atom must participate in at least one potential.
a) An interaction between one type/group and every other type/group is not required. The user must be aware of which interactions are considered.
  • It is very important to make sure that the atom types/groups in the xyz.in file are consistent with the potential file.

Related keywords

potential_definition