lammps/doc/fix_wall_reflect.txt

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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 to the args
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.

IMPORTANT NOTE: This fix performs its operations at the same point in
the timestep as other time integration fixes, such as "fix
nve"_fix_nve.html, "fix nvt"_fix_nvt.html, or "fix npt"_fix_npt.html.
Thus fix wall/reflect should normally be the last such fix specified
in the input script, since the adjustments it makes to atom
coordinates should come after the changes made by time integration.
LAMMPS will warn you if your fixes are not ordered this way.

[Restrictions:]

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

[Related commands:]

"fix wall/lj93"_fix_wall_lj93.html command

[Default:] none