Syntax:
compute ID group-ID group/groups/atom group2-ID group3-ID ... groupN-ID
Examples:
compute 1 lower group/groups/atom upper compute 2 lower group/groups/atom lower upper
Description:
Define a computation that calculates the total interaction energy and force between different groups of atoms. This group functions similarly to compute group/group, but additionally will calculate multiple group interactions and produces per-atom data. Interaction energy and forces are limited to pairwise interactions, so this compute is best applied to groups that do not contain intramolecular interactions (i.e. Bonds, Angles). If the aggregate interaction energy and force between only two groups is sought, compute group/group is a more efficient option.
The energy and force are calculated by looping over a neighbor list of pairwise interactions. Thus it can be inefficient to compute this quantity too frequently.
Output info:
This compute produces both a global vector and per-atom data. The size of the global vector depends on the number of other groups specified, N, producing 4(N+1) values. Each set of 4 values contain the interaction energy and the x, y, and z components of the force vector. The last 4 columns represent the total pairwise interaction energy and force of all specified groups with the compute group. Per-atom columns are similarly organized. See this section for an overview of LAMMPS output options.
All values calculated by this compute are "extensive". Vector values and per-atom columns 4n are interaction energy, in energy units. Vector and per-atom columns 4(n+1), 4(n+2), and 4(n+3) are in force units.
Restrictions:
Only pairwise interactions, as defined by the pair_style command, are included in this calculation. Bond (angle, dihedral, etc) interactions between atoms in the two groups are not included. Long-range interactions due to a kspace_style command are also not included. Not all pair potentials can be evaluated in a pairwise mode as required by this compute. For example, 3-body potentials, such as Tersoff and Stillinger-Weber cannot be used. EAM potentials for metals only include the pair potential portion of the EAM interaction, not the embedding term.
Related commands: compute group/group
Default: none