Syntax:
fix ID group-ID mvv/dpd lambda
fix ID group-ID mvv/edpd lambda
fix ID group-ID mvv/tdpd lambda
Examples:
fix 1 all mvv/dpd fix 1 all mvv/dpd 0.5 fix 1 all mvv/edpd fix 1 all mvv/edpd 0.5 fix 1 all mvv/tdpd fix 1 all mvv/tdpd 0.5
Description:
Perform time integration using the modified velocity-Verlet (MVV) algorithm to update position and velocity (fix mvv/dpd), or position, velocity and temperature (fix mvv/edpd), or position, velocity and concentration (fix mvv/tdpd) for particles in the group each timestep.
The modified velocity-Verlet (MVV) algorithm aims to improve the stability of the time integrator by using an extrapolated version of the velocity for the force evaluation:
where the parameter λ depends on the specific choice of DPD parameters, and needs to be tuned on a case-by-case basis. Specification of a lambda value is optional. If specified, the setting must be from 0.0 to 1.0. If not specified, a default value of 0.5 is used, which effectively reproduces the standard velocity-Verlet (VV) scheme. For more details, see Groot.
Fix mvv/dpd updates the position and velocity of each atom. It can be used with the pair_style mdpd command or other pair styles such as pair dpd.
Fix mvv/edpd updates the per-atom temperature, in addition to position and velocity, and must be used with the pair_style edpd command.
Fix mvv/tdpd updates the per-atom chemical concentration, in addition to position and velocity, and must be used with the pair_style tdpd command.
Restart, fix_modify, output, run start/stop, minimize info:
No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.
Restrictions:
This fix is part of the USER-MESO package. It is only enabled if LAMMPS was built with that package. See the Build package doc page for more info.
Related commands:
pair_style mdpd, pair_style edpd, pair_style tdpd
Default:
The default value for the optional lambda parameter is 0.5.
(Groot) Groot and Warren, J Chem Phys, 107: 4423-4435 (1997). DOI: 10.1063/1.474784