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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>
</CENTER>
<HR>
<H3>compute temp/sphere command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID temp/sphere bias-ID
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>temp/sphere = style name of this compute command
<LI>bias-ID = ID of a temperature compute that removes a velocity bias (optional)
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all temp/sphere
compute myTemp mobile temp/sphere tempCOM
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that calculates the temperature of a group of
spherical particles, including a contribution from both their
translational and rotational kinetic energy. This differs from the
usual <A HREF = "compute_temp.html">compute temp</A> command, which assumes point
particles with only translational kinetic energy.
</P>
<P>For 3d spherical particles, each has 6 degrees of freedom (3
translational, 3 rotational). For 2d spherical particles, each has 3
degrees of freedom (2 translational, 1 rotational).
</P>
<P>The translational kinetic energy is computed the same as is described
by the <A HREF = "compute_temp.html">compute temp</A> command. The rotational
kinetic energy is computed as 1/2 I w^2, where I is the moment of
inertia for a sphere and w is the particle's angular velocity.
</P>
<P>IMPORTANT NOTE: For <A HREF = "dimension.html">2d models</A>, particles are treated
as spheres, not disks, meaning their moment of inertia will be the
same as in 3d.
</P>
<P>A 6-component kinetic energy tensor is also calculated by this
compute. The formula for the components of the tensor is the same as
the above formula, except that v^2 and w^2 are replaced by vx*vy and
wx*wy for the xy component.
</P>
<P>The number of atoms contributing to the temperature is assumed to be
constant for the duration of the run; use the <I>dynamic</I> option of the
<A HREF = "compute_modify.html">compute_modify</A> command if this is not the case.
</P>
<P>If a <I>bias-ID</I> is specified it must be the ID of a temperature compute
that removes a "bias" velocity from each atom. This allows compute
temp/sphere to compute its thermal temperature after the translational
kinetic energy components have been altered in a prescribed way,
e.g. to remove a velocity profile. Thermostats that use this compute
will work with this bias term. See the doc pages for individual
computes that calculate a temperature and the doc pages for fixes that
perform thermostatting for more details.
</P>
<P>This compute subtracts out translational degrees-of-freedom due to
fixes that constrain molecular motion, such as <A HREF = "fix_shake.html">fix
shake</A> and <A HREF = "fix_rigid.html">fix rigid</A>. This means the
temperature of groups of atoms that include these constraints will be
computed correctly. If needed, the subtracted degrees-of-freedom can
be altered using the <I>extra</I> option of the
<A HREF = "compute_modify.html">compute_modify</A> command.
</P>
<P>See <A HREF = "Section_howto.html#4_16">this howto section</A> of the manual for a
discussion of different ways to compute temperature and perform
thermostatting.
</P>
<P><B>Output info:</B>
</P>
<P>The scalar value calculated by this compute is "intensive", meaning it
is independent of the number of atoms in the simulation. The vector
values are "extensive", meaning they scale with the number of atoms in
the simulation.
</P>
<P><B>Restrictions:</B>
</P>
<P>This compute requires that particles be represented as extended
spheres and not point particles. This means they will have an angular
velocity and a diameter which is determined either by the
<A HREF = "shape.html">shape</A> command or by each particle being assigned an
individual radius, e.g. for <A HREF = "atom_style.html">atom_style granular</A>.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "compute_temp.html">compute temp</A>, <A HREF = "compute_temp.html">compute
temp/asphere</A>
</P>
<P><B>Default:</B> none
</P>
</HTML>
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