"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)

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fix mvv/dpd command :h3
fix mvv/edpd command :h3
fix mvv/tdpd command :h3

[Syntax:]

fix ID group-ID mvv/dpd lambda :pre
fix ID group-ID mvv/edpd lambda :pre
fix ID group-ID mvv/tdpd lambda :pre

ID, group-ID are documented in "fix"_fix.html command
mvv/dpd, mvv/edpd, mvv/tdpd = style name of this fix command
lambda = (optional) relaxation parameter (unitless) :ul

[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 :pre

[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:

:c,image(Eqs/fix_mvv_dpd.jpg)

where the parameter <font size="4">&lambda;</font> 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"_#Groot2.

Fix {mvv/dpd} updates the position and velocity of each atom.  It can
be used with the "pair_style mdpd"_pair_meso.html command or other
pair styles such as "pair dpd"_pair_dpd.html.

Fix {mvv/edpd} updates the per-atom temperature, in addition to
position and velocity, and must be used with the "pair_style
edpd"_pair_meso.html 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"_pair_meso.html command.

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[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  None of the "fix_modify"_fix_modify.html options
are relevant to this fix.  No global or per-atom quantities are stored
by this fix for access by various "output commands"_Howto_output.html.
No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.  This fix is not invoked during "energy
minimization"_minimize.html.

[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"_Build_package.html doc page for more info.

[Related commands:]

"pair_style mdpd"_pair_meso.html, "pair_style edpd"_pair_meso.html,
"pair_style tdpd"_pair_meso.html

[Default:]

The default value for the optional {lambda} parameter is 0.5.

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:link(Groot2)
[(Groot)] Groot and Warren, J Chem Phys, 107: 4423-4435 (1997).  DOI:
10.1063/1.474784

