LAMMPS WWW Site - LAMMPS Documentation - LAMMPS Commands

### compute pe command

### compute pe/cuda command

Syntax:

    compute ID group-ID pe keyword ...

- ID, group-ID are documented in compute command
- pe = style name of this compute command
- zero or more keywords may be appended
- keyword = pair or bond or angle or dihedral or improper or kspace

Examples:

    compute 1 all pe
    compute molPE all pe bond angle dihedral improper

Description:

Define a computation that calculates the potential energy of the entire system of atoms. The specified group must be "all". See the compute pe/atom command if you want per-atom energies. These per-atom values could be summed for a group of atoms via the compute reduce command.

The 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, improper, and kspace (long-range) energy. If any extra keywords are listed, then only those components are summed to compute the potential energy.

The Kspace contribution requires 1 extra FFT each timestep the energy is calculated, if using the PPPM solver via the kspace_style pppm command. Thus it can increase the cost of the PPPM calculation if it is needed on a large fraction of the simulation timesteps.

Various fixes can contribute to the total potential energy of the system. See the doc pages for individual fixes for details. The thermo option of the compute_modify command determines whether these contributions are added into the computed potential energy. If no keywords are specified the default is yes. If any keywords are specified, the default is no.

A compute of this style with the ID of "thermo_pe" is created when LAMMPS starts up, as if this command were in the input script:

    compute thermo_pe all pe

See the "thermo_style" command for more details.

Styles with a cuda suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed in Section_accelerate of the manual. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the USER-CUDA package. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See Section_accelerate of the manual for more instructions on how to use the accelerated styles effectively.

Output info:

This compute calculates a global scalar (the potential energy). This value can be used by any command that uses a global scalar value from a compute as input. See Section_howto 15 for an overview of LAMMPS output options.

The scalar value calculated by this compute is "extensive". The scalar value will be in energy units.

Restrictions: none

Related commands:

compute pe/atom

Default: none