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# fix dpd/energy command

Accelerator Variants: dpd/energy/kk

## Syntax

    fix ID group-ID dpd/energy

- ID, group-ID are documented in fix command

- dpd/energy = style name of this fix command

## Examples

    fix 1 all dpd/energy

## Description

Perform constant energy dissipative particle dynamics (DPD-E) integration. This fix updates the internal energies for particles in the group at each timestep. It must be used in conjunction with a deterministic integrator (e.g. fix nve) that updates the particle positions and velocities.

For fix dpd/energy, the particle internal temperature is related to the particle internal energy through a mesoparticle equation of state. An additional fix must be specified that defines the equation of state for each particle, e.g. fix eos/cv.

This fix must be used with the pair_style dpd/fdt/energy command.

Note that numerous variants of DPD can be specified by choosing an appropriate combination of the integrator and pair_style dpd/fdt/energy command. DPD under isoenergetic conditions can be specified by using fix dpd/energy, fix nve and pair_style dpd/fdt/energy. DPD under isoenthalpic conditions can be specified by using fix dpd/energy, fix nph and pair_style dpd/fdt/energy. Examples of each DPD variant are provided in the examples/PACKAGES/dpd-react directory.

Styles with a gpu, intel, kk, omp, or opt 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 on the Accelerator packages page. 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 GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page 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 the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

## Restrictions

This command is part of the DPD-REACT package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

This fix must be used with an additional fix that specifies time integration, e.g. fix nve.

The fix dpd/energy requires the dpd atom_style to be used in order to properly account for the particle internal energies and temperature.

The fix dpd/energy must be used with an additional fix that specifies the mesoparticle equation of state for each particle.

## Related commands

fix nve fix eos/cv

## Default

none

(Lisal) M. Lisal, J.K. Brennan, J. Bonet Avalos, J. Chem. Phys., 135, 204105 (2011).

(Larentzos) J.P. Larentzos, J.K. Brennan, J.D. Moore, and W.D. Mattson, ARL-TR-6863, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD (2014).