# fix dpd/energy command

## 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/USER/dpd directory.

## Restrictions

This command is part of the USER-DPD package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section 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.