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<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_modify command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix_modify fix-ID keyword value ...
</PRE>
<UL><LI>fix-ID = ID of the fix to modify
<LI>one or more keyword/value pairs may be appended
<LI>keyword = <I>temp</I> or <I>press</I> or <I>energy</I>
<PRE> <I>temp</I> value = compute ID that calculates a temperature
<I>press</I> value = compute ID that calculates a pressure
<I>energy</I> value = <I>yes</I> or <I>no</I>
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix_modify 3 temp myTemp press myPress
fix_modify 1 energy yes
</PRE>
<P><B>Description:</B>
</P>
<P>Modify one or more parameters of a previously defined fix. Only
specific fix styles support specific parameters. See the doc pages
for individual fix commands for info on which ones support which
fix_modify parameters.
</P>
<P>The <I>temp</I> keyword is used to determine how a fix computes
temperature. The specified compute ID must have been previously
defined by the user via the <A HREF = "compute.html">compute</A> command and it must
be a style of compute that calculates a temperature. All fixes that
compute temperatures define their own compute by default, as described
in their documentation. Thus this option allows the user to override
the default method for computing T.
</P>
<P>The <I>press</I> keyword is used to determine how a fix computes pressure.
The specified compute ID must have been previously defined by the user
via the <A HREF = "compute.html">compute</A> command and it must be a style of
compute that calculates a pressure. All fixes that compute pressures
define their own compute by default, as described in their
documentation. Thus this option allows the user to override the
default method for computing P.
</P>
<P>For fixes that calculate a contribution to the potential energy of the
system, the <I>energy</I> keyword will include that contribution in
thermodynamic output of potential energy. See the
<A HREF = "thermo_style.html">thermo_style</A> command for info on how potential
energy is output. The contribution by itself can be printed by using
the keyword f_ID in the thermo_style custom command, where ID is the
fix-ID of the appropriate fix. Note that you must use this setting
for a fix if you are using it when performing an <A HREF = "minimize.html">energy
minimization</A> and if you want the energy and forces it
produces to be part of the optimization criteria.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix.html">fix</A>, <A HREF = "compute_temp.html">compute temp</A>, <A HREF = "compute_pressure.html">compute
pressure</A>, <A HREF = "thermo_style.html">thermo_style</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are temp = ID defined by fix, press = ID defined
by fix, energy = no.
</P>
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