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

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

:line

fix nve/limit command :h3

[Syntax:]

fix ID group-ID nve/limit xmax :pre

ID, group-ID are documented in "fix"_fix.html command
nve = style name of this fix command
xmax = maximum distance an atom can move in one timestep (distance units) :ul

[Examples:]

fix 1 all nve/limit 0.1 :pre

[Description:]

Perform constant NVE updates of position and velocity for atoms in the
group each timestep.  A limit is imposed on the maximum distance an
atom can move in one timestep.  This is useful when starting a
simulation with a configuration containing highly overlapped atoms.
Normally this would generate huge forces which would blow atoms out of
the simulation box, causing LAMMPS to stop with an error.

Using this fix can overcome that problem.  Forces on atoms must still
be computable (which typically means 2 atoms must have a separation
distance > 0.0).  But large velocities generated by large forces are
reset to a value that corresponds to a displacement of length {xmax}
in a single timestep.  {Xmax} is specified in distance units; see the
"units"_units.html command for details.  The value of {xmax} should be
consistent with the neighbor skin distance and the frequency of
neighbor list re-building, so that pairwise interactions are not
missed on successive timesteps as atoms move.  See the
"neighbor"_neighbor.html and "neigh_modify"_neigh_modify.html commands
for details.

Note that if a velocity reset occurs the integrator will not conserve
energy.  On steps where no velocity resets occur, this integrator is
exactly like the "fix nve"_fix_nve.html command.  Since forces are
unaltered, pressures computed by thermodynamic output will still be
very large for overlapped configurations.

[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 scalar or vector or per-atom
quantities are stored by this fix for access by various "output
commands"_Section_howto.html#4_15.  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:] none

[Related commands:]

"fix nve"_fix_nve.html, "fix nve/noforce"_fix_nve_noforce.html,
"pair_style soft"_pair_soft.html

[Default:] none
