"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 wall/reflect command :h3

[Syntax:]

fix ID group-ID wall/reflect keyword ... :pre

ID, group-ID are documented in "fix"_fix.html command
wall/reflect = style name of this fix command
one or more keyword/value pairs may be appended
keyword = {xlo} or {xhi} or {ylo} or {yhi} or {zlo} or {zhi} :ul

[Examples:]

fix xwalls all wall/reflect xlo xhi
fix walls all wall/reflect xlo ylo zlo xhi yhi zhi :pre

[Description:]

Bound the simulation with one or more walls which reflect particles
when they attempt to move thru them. 

Reflection means that if an atom moves outside the box on a timestep
by a distance delta (e.g. due to "fix nve"_fix_nve.html), then it is
put back inside the box by the same delta and the sign of the
corresponding component of its velocity is flipped.

When used in conjunction with "fix nve"_fix_nve.html and "run_style
verlet"_run_style.html, the resultant time-integration algorithm is
equivalent to the primitive splitting algorithm (PSA) described by
"Bond"_#Bond.  Because each reflection event divides
the corresponding timestep asymmetrically, energy conservation is only
satisfied to O(dt), rather than to O(dt^2) as it would be for
velocity-Verlet integration without reflective walls.

[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:]

Any dimension (xyz) that has a reflecting wall must be non-periodic.

A reflecting wall should not be used with rigid bodies such as those
defined by a "fix rigid" command.  This is because the wall/reflect
displaces atoms directly rather than exerts a force on them.  For
rigid bodies, use a soft wall instead, such as "fix
wall/lj93"_fix_wall_lj93.html.  LAMMPS will flag the use of a rigid
fix with fix wall/reflect with a warning, but will not generate an
error.

[Related commands:]

"fix wall/lj93"_fix_wall_lj93.html command

[Default:] none

:link(Bond)
[(Bond)] Bond and Leimkuhler, SIAM J Sci Comput, 30, p 134 (2007).
