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