2006-09-22 00:22:34 +08:00
|
|
|
<HTML>
|
|
|
|
|
<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
|
|
|
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<H3>fix momentum command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>fix ID group-ID momentum N keyword values ...
|
|
|
|
|
</PRE>
|
|
|
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
|
|
|
|
|
|
<LI>momentum = style name of this fix command
|
|
|
|
|
|
2006-10-03 04:21:36 +08:00
|
|
|
<LI>N = adjust the momentum every this many timesteps
|
2007-07-03 04:04:44 +08:00
|
|
|
one or more keyword/value pairs may be appended
|
2006-09-22 00:22:34 +08:00
|
|
|
|
|
|
|
|
<LI>keyword = <I>linear</I> or <I>angular</I>
|
|
|
|
|
|
|
|
|
|
<PRE> <I>linear</I> values = xflag yflag zflag
|
|
|
|
|
xflag,yflag,zflag = 0/1 to exclude/include each dimension
|
|
|
|
|
<I>angular</I> values = none
|
|
|
|
|
</PRE>
|
|
|
|
|
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
2006-10-03 04:21:36 +08:00
|
|
|
<PRE>fix 1 all momentum 1 linear 1 1 0
|
|
|
|
|
fix 1 all momentum 100 linear 1 1 1 angular
|
2006-09-22 00:22:34 +08:00
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Zero the linear and/or angular momentum of the group of atoms every N
|
2006-10-03 04:21:36 +08:00
|
|
|
timesteps by adjusting the velocities of the atoms. One (or both) of
|
|
|
|
|
the <I>linear</I> or <I>angular</I> keywords must be specified.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
|
|
|
|
<P>If the <I>linear</I> keyword is used, the linear momentum is zeroed by
|
|
|
|
|
subtracting the center-of-mass velocity of the group from each atom.
|
|
|
|
|
This does not change the relative velocity of any pair of atoms. One
|
|
|
|
|
or more dimensions can be excluded from this operation by setting the
|
|
|
|
|
corresponding flag to 0.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If the <I>angular</I> keyword is used, the angular momentum is zeroed by
|
|
|
|
|
subtracting a rotational component from each atom.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This command can be used to insure the entire collection of atoms (or
|
|
|
|
|
a subset of them) does not drift or rotate during the simulation due
|
|
|
|
|
to random perturbations (e.g. <A HREF = "fix_langevin.html">fix langevin</A>
|
|
|
|
|
thermostatting).
|
|
|
|
|
</P>
|
|
|
|
|
<P>Note that the <A HREF = "velocity.html">velocity</A> command can be used to create
|
2006-10-03 04:21:36 +08:00
|
|
|
initial velocities with zero aggregate linear and/or angular momentum.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
2007-06-26 08:03:39 +08:00
|
|
|
<P><B>Restart, fix_modify, thermo output, run start/stop, minimize info:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
|
|
|
|
|
files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
|
|
|
|
|
are relevant to this fix. No quantities calculated by this fix can be
|
|
|
|
|
output by the <A HREF = "thermo_style.html">thermo_style custom</A> command. No
|
|
|
|
|
parameter of this fix can be used with the <I>start/stop</I> keywords of
|
|
|
|
|
the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
|
|
|
|
|
minimization</A>.
|
|
|
|
|
</P>
|
2006-09-22 00:22:34 +08:00
|
|
|
<P><B>Restrictions:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P><A HREF = "fix_recenter.html">fix recenter</A>, <A HREF = "velocity.html">velocity</A>
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
