# fix dpd/energy command

Accelerator Variants: *dpd/energy/kk*

## Syntax

    fix ID group-ID dpd/energy

-   ID, group-ID are documented in [fix](fix) command
-   dpd/energy = style name of this fix command

## Examples

``` LAMMPS
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](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](fix_eos_cv).

This fix must be used with the [pair_style dpd/fdt/energy](pair_style)
command.

Note that numerous variants of DPD can be specified by choosing an
appropriate combination of the integrator and [pair_style
dpd/fdt/energy](pair_style) 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](Speed_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](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](Run_options) when you invoke LAMMPS, or you can use the
[suffix](suffix) command in your input script.

See the [Accelerator packages](Speed_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](Build_package) page for more info.

This fix must be used with an additional fix that specifies time
integration, e.g. [fix nve](fix_nve).

The fix *dpd/energy* requires the *dpd* [atom_style](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_nve) [fix eos/cv](fix_eos_cv)

## Default

none

------------------------------------------------------------------------

::: {#Lisal1}
**(Lisal)** M. Lisal, J.K. Brennan, J. Bonet Avalos, \"Dissipative
particle dynamics at isothermal, isobaric, isoenergetic, and
isoenthalpic conditions using Shardlow-like splitting algorithms.\", J.
Chem. Phys., 135, 204105 (2011).
:::

::: {#Larentzos3}
**(Larentzos)** J.P. Larentzos, J.K. Brennan, J.D. Moore, and W.D.
Mattson, \"LAMMPS Implementation of Constant Energy Dissipative Particle
Dynamics (DPD-E)\", ARL-TR-6863, U.S. Army Research Laboratory, Aberdeen
Proving Ground, MD (2014).
:::