forked from lijiext/lammps
77 lines
3.0 KiB
HTML
77 lines
3.0 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>compute temp/region command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>compute ID group-ID temp/region region-ID
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
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<LI>temp/region = style name of this compute command
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<LI>region-ID = ID of region to use for choosing atoms
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>temperature mine flow region boundary
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define a computation that calculates the temperature of a group of
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atoms in a geometric region. This can be useful for thermostatting
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one portion of the simulation box. E.g. a McDLT simulation where one
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side is cooled, and the other side is heated. A compute of this style
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can be used by any command that computes a temperature,
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e.g. <A HREF = "thermo_modify.html">thermo_modify</A>, <A HREF = "fix_temp_rescale.html">fix
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temp/rescale</A>, etc.
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</P>
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<P>Note that a <I>region</I>-style temperature can be used to thermostat with
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<A HREF = "fix_temp_rescale.html">fix temp/rescale</A> or <A HREF = "fix_langevin.html">fix
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langevin</A>, but should probably not be used with
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Nose/Hoover style fixes (<A HREF = "fix_nvt.html">fix nvt</A>, <A HREF = "fix_npt.html">fix
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npt</A>, or <A HREF = "fix_nph.html">fix nph</A>), if the
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degrees-of-freedom included in the computed T varies with time.
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</P>
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<P>The temperature is calculated by the formula KE = dim/2 N k T, where
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KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2),
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dim = 2 or 3 = dimensionality of the simulation, N = number of atoms
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in both the group and region, k = Boltzmann constant, and T =
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temperature.
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</P>
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<P>A 6-component kinetic energy tensor is also calculated by this compute
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for use in the computation of a pressure tensor. The formula for the
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components of the tensor is the same as the above formula, except that
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v^2 is replaced by vx * vy for the xy component, etc.
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</P>
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<P>The number of atoms contributing to the temperature is compute each
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time the temperature is evaluated since it is assumed atoms can
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enter/leave the region. Thus there is no need to use the <I>dynamic</I>
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option of the <A HREF = "compute_modify.html">compute_modify</A> command for this
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compute style.
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</P>
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<P>Unlike other compute styles that calculate temperature, this compute
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does NOT currently subtract out degrees-of-freedom due to fixes that
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constrain molecular motion, such as <A HREF = "fix_shake.html">fix shake</A> and
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<A HREF = "fix_rigid.html">fix rigid</A>. If needed the subtracted
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degrees-of-freedom can be altered using the <I>extra</I> option of the
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<A HREF = "compute_modify.html">compute_modify</A> command.
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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 = "compute_temp.html">compute temp</A>, <A HREF = "compute_pressure.html">compute
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pressure</A>
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</P>
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<P><B>Default:</B> none
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</P>
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