forked from lijiext/lammps
112 lines
4.4 KiB
HTML
112 lines
4.4 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 temp/rescale command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>fix ID group-ID temp/rescale N Tstart Tstop window fraction keyword values ...
|
|
</PRE>
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
<LI>temp/rescale = style name of this fix command
|
|
|
|
<LI>N = perform rescaling every N steps
|
|
|
|
<LI>Tstart,Tstop = desired temperature at start/end of run (temperature units)
|
|
|
|
<LI>window = only rescale if temperature is outside this window (temperature units)
|
|
|
|
<LI>fraction = rescale to target temperature by this fraction
|
|
|
|
<LI>zero or more keyword/value pairs may be appended to the args
|
|
|
|
<PRE>keyword = <I>region</I>
|
|
<I>region</I> values = region-ID
|
|
region-ID = ID of region to apply rescaling to
|
|
</PRE>
|
|
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>fix 3 flow temp/rescale 100 1.0 1.1 0.02 0.5
|
|
fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0 region edge
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Reset the temperature of a group of atoms by explicitly rescaling
|
|
their velocities.
|
|
</P>
|
|
<P>Rescaling is performed every N timesteps. The target temperature is a
|
|
ramped value between the <I>Tstart</I> and <I>Tstop</I> temperatures at the
|
|
beginning and end of the run. The <A HREF = "run.html">run</A> command documents
|
|
how to make the ramping take place across multiple runs.
|
|
</P>
|
|
<P>Rescaling is only performed if the difference between the current and
|
|
desired temperatures is greater than the <I>window</I> value. The amount
|
|
of rescaling that is applied is a <I>fraction</I> (from 0.0 to 1.0) of the
|
|
difference between the actual and desired temperature. E.g. if
|
|
<I>fraction</I> = 1.0, the temperature is reset to exactly the desired
|
|
value.
|
|
</P>
|
|
<P>The keyword <I>region</I> applies the fix only to atoms that are in the
|
|
specified geometric region (and in the fix group). Since atoms can
|
|
enter/leave a region, this test is performed each timestep.
|
|
</P>
|
|
<P>This fix computes a temperature each timestep. The fix creates its
|
|
own method for computing T, as if it had been defined by one of these
|
|
commands:
|
|
</P>
|
|
<PRE>temperature fix-ID group-ID full
|
|
temperature fix-ID group-ID region region-ID
|
|
</PRE>
|
|
<P>Which is used depends on whether a region was specified with the fix.
|
|
See the <A HREF = "temperature.html">temperature</A> command for details. Note that
|
|
this is NOT the temperature with ID = <I>default</I>. This means you can
|
|
change the attributes of this fix's temperature (e.g. its
|
|
degrees-of-freedom) via the <A HREF = "temp_modify.html">temp_modify</A> command or
|
|
print the temperature with thermodyanmic output via the <A HREF = "thermo_style.html">thermo_style
|
|
custom</A> command using the appropriate temp-ID =
|
|
fix-ID. It also means that changing attributes of the default
|
|
temperature will have no effect on this fix. Alternatively, you can
|
|
directly assign a new temperature to the fix via the
|
|
<A HREF = "fix_modify.html">fix_modify</A> command. For consistency, if using the
|
|
keyword <I>region</I>, the temperature you assign should also be of style
|
|
<I>region</I>.
|
|
</P>
|
|
<P>A temp/rescale fix does not update the coordinates of its atoms. It
|
|
is normally used with a fix of style <I>nve</I> that does that. A
|
|
temp/rescale fix should not normally be used on atoms that also have
|
|
their temperature controlled by another fix - e.g. a
|
|
<A HREF = "fix_nvt.html">nvt</A> or <A HREF = "fix_langevin.html">langevin</A> fix.
|
|
</P>
|
|
<P>This fix supports the <A HREF = "fix_modify.html">fix_modify</A> options for
|
|
<I>thermo</I> and <I>energy</I>. The former will print the contribution the fix
|
|
makes to the energy of the system when thermodynamics is printed. The
|
|
latter will add this contribution to the total potential energy
|
|
(PotEng) so that energy conservation can be monitored. Note that the
|
|
energy value printed by thermo is not cummulative energy, but energy
|
|
added in the most recent rescaling. Also note that because this fix
|
|
is invoked every N steps and thermo may be printed every M steps, that
|
|
unless M is a multiple of N, the energy info printed by thermo will
|
|
not be for the current timestep.
|
|
</P>
|
|
<P><B>Restrictions:</B> none
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
</P>
|
|
<P><A HREF = "fix_langevin.html">fix langevin</A>, <A HREF = "fix_nvt.html">fix nvt</A>,
|
|
<A HREF = "fix_modify.html">fix_modify</A>
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
</HTML>
|