fix shardlow command — LAMMPS documentation

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# fix shardlow command

Accelerator Variants: shardlow/kk

## Syntax

    fix ID group-ID shardlow

- ID, group-ID are documented in fix command

- shardlow = style name of this fix command

## Examples

    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 or fix nph). 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) and (Larentzos1).

The fix shardlow must be used with the pair_style dpd/fdt or pair_style dpd/fdt/energy 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 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 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 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 or fix nph.

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, fix eos/cv

## Default

none

(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).

(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).

(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).