Syntax:
compute ID group-ID pe/atom keyword ...
Examples:
compute 1 all pe/atom compute 1 all pe/atom pair compute 1 all pe/atom pair bond
Description:
Define a computation that computes the per-atom potential energy for each atom in a group. See the compute pe command if you want the potential energy of the entire system.
The per-atom energy is calculated by the various pair, bond, etc potentials defined for the simulation. If no extra keywords are listed, then the potential energy is the sum of pair, bond, angle, dihedral, and improper energy. If any extra keywords are listed, then only those components are summed to compute the potential energy.
Note that the energy of each atom is due to its interaction with all other atoms in the simulation, not just with other atoms in the group.
For an energy contribution produced by a small set of atoms (e.g. 4 atoms in a dihedral or 3 atoms in a Tersoff 3-body interaction), that energy is assigned in equal portions to each atom in the set. E.g. 1/4 of the dihedral energy to each of the 4 atoms.
The dihedral_style charmm style calculates pairwise interactions between 1-4 atoms. The energy contribution of these terms is included in the pair energy, not the dihedral energy.
As an example of per-atom potential energy compared to total potential energy, these lines in an input script should yield the same result in the last 2 columns of thermo output:
compute peratom all pe/atom compute pe all reduce sum c_peratom thermo_style custom step temp etotal press pe c_pe
IMPORTANT NOTE: The per-atom energy does NOT include contributions due to long-range Coulombic interactions (via the kspace_style command). It's not clear this contribution can easily be computed. It also does not include any Lennard-Jones tail corrections invoked by the pair_modify tail yes command, since those are global contributions to the system energy.
Output info:
This compute calculates a per-atom vector, which can be accessed by any command that uses per-atom values from a compute as input. See Section_howto 15 for an overview of LAMMPS output options.
The per-atom vector values will be in energy units.
Restrictions:
Related commands:
compute pe, compute stress/atom
Default: none