# fix shardlow command

Accelerator Variants: *shardlow/kk*

## Syntax

    fix ID group-ID shardlow

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

## Examples

``` LAMMPS
fix 1 all shardlow
```

## Description

Specifies that the Shardlow splitting algorithm (SSA) is to be used to
integrate the DPD equations of motion. The SSA splits the integration
into a stochastic and deterministic integration step. The fix *shardlow*
performs the stochastic integration step and must be used in conjunction
with a deterministic integrator (e.g. [fix nve](fix_nve) or [fix
nph](fix_nh)). The stochastic integration of the dissipative and random
forces is performed prior to the deterministic integration of the
conservative force. Further details regarding the method are provided in
[(Lisal)](Lisal) and [(Larentzos1)](Larentzos1sh).

The fix *shardlow* must be used with the [pair_style
dpd/fdt](pair_style) or [pair_style dpd/fdt/energy](pair_style) command
to properly initialize the fluctuation-dissipation theorem parameter(s)
sigma (and kappa, if necessary).

Note that numerous variants of DPD can be specified by choosing an
appropriate combination of the integrator and [pair_style
dpd/fdt](pair_style) command. DPD under isothermal conditions can be
specified by using fix *shardlow*, fix *nve* and pair_style *dpd/fdt*.
DPD under isoenergetic conditions can be specified by using fix
*shardlow*, fix *nve* and pair_style *dpd/fdt/energy*. DPD under
isobaric conditions can be specified by using fix shardlow, fix *nph*
and pair_style *dpd/fdt*. DPD under isoenthalpic conditions can be
specified by using fix shardlow, 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 is currently limited to orthogonal simulation cell geometries.

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

The Shardlow splitting algorithm requires the sizes of the subdomain
lengths to be larger than twice the cutoff+skin. Generally, the domain
decomposition is dependent on the number of processors requested.

## Related commands

[pair_style dpd/fdt](pair_dpd_fdt), [fix eos/cv](fix_eos_cv)

## Default

none

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

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

::: {#Larentzos1sh}
**(Larentzos1)** J.P. Larentzos, J.K. Brennan, J.D. Moore, M. Lisal and
W.D. Mattson, \"Parallel Implementation of Isothermal and Isoenergetic
Dissipative Particle Dynamics Using Shardlow-Like Splitting
Algorithms\", Comput. Phys. Commun., 185, 1987-1998 (2014).
:::

::: {#Larentzos2sh}
**(Larentzos2)** 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).
:::