forked from lijiext/lammps
97 lines
3.3 KiB
HTML
97 lines
3.3 KiB
HTML
<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 smd/setvel command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>fix ID group-ID smd/setvel vx vy vz keyword value ...
|
|
</PRE>
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
<LI>smd/setvel = style name of this fix command
|
|
|
|
<LI>vx,vy,vz = velocity component values
|
|
|
|
<LI>any of vx,vy,vz can be a variable (see below)
|
|
|
|
<LI>zero or more keyword/value pairs may be appended to args
|
|
|
|
<LI>keyword = <I>region</I>
|
|
|
|
<PRE> <I>region</I> value = region-ID
|
|
region-ID = ID of region particles must be in to have their velocities set
|
|
</PRE>
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>fix top_velocity top_group setvel 1.0 0.0 0.0
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Set each component of velocity on each particle in the group to the specified
|
|
values vx,vy,vz, regardless of the forces acting on the particle. This command can
|
|
be used to impose velocity boundary conditions.
|
|
</P>
|
|
<P>Any of the vx,vy,vz values can be specified as NULL which means do not
|
|
alter the velocity component in that dimension.
|
|
</P>
|
|
<P>This fix is indented to be used together with a time integration fix.
|
|
</P>
|
|
<P>Any of the 3 quantities defining the velocity components can be specified
|
|
as an equal-style or atom-style <A HREF = "variable.html">variable</A>, namely <I>vx</I>,
|
|
<I>vy</I>, <I>vz</I>. If the value is a variable, it should be specified as
|
|
v_name, where name is the variable name. In this case, the variable
|
|
will be evaluated each timestep, and its value used to determine the
|
|
force component.
|
|
</P>
|
|
<P>Equal-style variables can specify formulas with various mathematical
|
|
functions, and include <A HREF = "thermo_style.html">thermo_style</A> command
|
|
keywords for the simulation box parameters and timestep and elapsed
|
|
time. Thus it is easy to specify a time-dependent velocity field.
|
|
</P>
|
|
<P>Atom-style variables can specify the same formulas as equal-style
|
|
variables but can also include per-atom values, such as atom
|
|
coordinates. Thus it is easy to specify a spatially-dependent velocity
|
|
field with optional time-dependence as well.
|
|
</P>
|
|
<P>If the <I>region</I> keyword is used, the particle must also be in the
|
|
specified geometric <A HREF = "region.html">region</A> in order to have its velocity set by this command.
|
|
</P>
|
|
<HR>
|
|
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
|
</P>
|
|
<P>Currently, no part of USER-SMD supports restarting nor minimization
|
|
None of the <A HREF = "fix_modify.html">fix_modify</A> options
|
|
are relevant to this fix.
|
|
</P>
|
|
<P>This fix computes a global 3-vector of forces, which can be accessed
|
|
by various <A HREF = "Section_howto.html#howto_15">output commands</A>. This is the
|
|
total force on the group of atoms. The vector values calculated by this
|
|
fix are "extensive".
|
|
</P>
|
|
<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
|
|
the <A HREF = "run.html">run</A> command.
|
|
</P>
|
|
<P><B>Restrictions:</B>
|
|
</P>
|
|
<P>This fix is part of the USER-SMD package. It is only enabled if
|
|
LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making LAMMPS</A>
|
|
section for more info.
|
|
</P>
|
|
<P><B>Related commands:</B> none
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
</HTML>
|