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140 lines
6.0 KiB
HTML
<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
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<LI>keyword = <I>region</I> or <I>partial</I>
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</UL>
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<PRE> <I>region</I> values = region-ID
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region-ID = ID of region to apply rescaling to
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<I>partial</I> values = xflag yflag zflag
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xflag,yflag,zflag = 0/1 if the velocity component should not or should be rescaled
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</PRE>
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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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fix 3 boundary temp/rescale 1 1.0 1.5 0.05 1.0 partial 0 1 1
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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.
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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>The keyword <I>partial</I> rescales only the specified velocity components.
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A compute of style temp/partial is used to compute the current
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temperature of just those components (see below).
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</P>
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<P>The <I>region</I> and <I>partial</I> keywords cannot currently be used together.
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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 computes a temperature each timestep. To do this, the fix
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creates its own compute of style "temp" or "temp/region" or
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"temp/partial", as if one of these commands had been issued:
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</P>
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<PRE>compute fix-ID_temp group-ID temp
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compute fix-ID_temp group-ID temp/region region-ID
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compute fix-ID_temp group-ID temp/partial xflag yflag zflag
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</PRE>
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<P>Which is used depends on whether the <I>region</I> or <I>partial</I> keywords
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were specified with the fix. See the <A HREF = "compute_temp.html">compute
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temp</A>, <A HREF = "compute_temp_region.html">compute
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temp/region</A>, and <A HREF = "compute_temp_partial.html">compute
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temp/partial</A> commands for details. Note
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that the ID of the new compute is the fix-ID with underscore + "temp"
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appended and the group for the new compute is the same as the fix
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group.
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</P>
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<P>Note that this is NOT the compute used by thermodynamic output (see
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the <A HREF = "thermo_style.html">thermo_style</A> command) with ID = <I>thermo_temp</I>.
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This means you can change the attributes of this fix's temperature
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(e.g. its degrees-of-freedom) via the
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<A HREF = "compute_modify.html">compute_modify</A> command or print this temperature
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during thermodyanmic output via the <A HREF = "thermo_style.html">thermo_style
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custom</A> command using the appropriate compute-ID.
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It also means that changing attributes of <I>thermo_temp</I> will have no
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effect on this fix.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>.
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</P>
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<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>temp</I> option is supported by this
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fix. You can use it to assign a <A HREF = "compute.html">compute</A> you have
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defined to this fix which will be used in its thermostatting
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procedure. For consistency, if using the keyword <I>region</I>, the
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compute you assign should also be of style
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<A HREF = "compute_temp_region.html">temp/region</A>.
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</P>
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<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
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fix to add the energy change implied by a velocity rescaling to the
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system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
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output</A>. Note that because this fix is invoked
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every N steps and thermodynamic info is printed every M steps, that
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unless M is a multiple of N, the energy contribution will be zero.
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</P>
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<P>The potential energy change due to this fix is stored as a scalar
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quantity, which can be accessed by various <A HREF = "Section_howto.html#4_15">output
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commands</A>.
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</P>
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<P>The energy change can be printed as part of thermodynamic output via
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the keyword f_ID, where ID is the fix-ID of this fix. See the
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<A HREF = "thermo_style.html">thermo_style custom</A> command for details.
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</P>
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<P>This fix can ramp its target temperature over multiple runs, using the
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<I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A> command. See the
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<A HREF = "run.html">run</A> command for details of how to do this.
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</P>
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<P>This fix is not invoked during <A HREF = "minimize.html">energy minimization</A>.
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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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