fix shardlow command

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/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 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 sub-domain 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).