2007-04-20 07:25:27 +08:00
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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/asphere 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/asphere
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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/asphere = style name of this compute command
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>compute 1 all temp/asphere
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compute myTemp mobile temp/asphere
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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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2008-03-18 08:23:39 +08:00
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aspherical particles, including a contribution from both their
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translational and rotational kinetic energy. This differs from the
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2008-03-19 04:39:07 +08:00
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usual <A HREF = "compute_temp.html">compute temp</A> command, which assumes point
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particles with only translational kinetic energy.
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2008-03-18 08:23:39 +08:00
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</P>
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<P>For 3d aspherical particles, each has 3, 5, or 6 degrees of freedom (3
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translational, remainder rotational), depending on whether the
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particle is spherical, uniaxial, or biaxial. This is determined by
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the <A HREF = "shape.html">shape</A> command. Uniaxial means two of its three shape
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2008-03-19 04:39:07 +08:00
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parameters are equal. Biaxial means all 3 shape parameters are
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different.
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2008-03-18 08:23:39 +08:00
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</P>
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2008-03-19 04:39:07 +08:00
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<P>For 2d aspherical particles, each has 3 or 4 degrees of freedom (3
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translational, remainder rotational), depending on whether the
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particle is spherical, or biaxial. Biaxial means the x,y shape
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parameters are unequal.
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2008-03-18 08:23:39 +08:00
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</P>
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<P>IMPORTANT NOTE: These degrees of freedom assume that the interaction
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potential between degenerate aspherical particles does not impart
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rotational motion to the extra degrees of freedom. E.g. the <A HREF = "pair_gayberne.html">GayBerne
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pair potential</A> does not impart torque to spherical
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particles, so they do not rotate.
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</P>
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2008-03-19 04:39:07 +08:00
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<P>The rotational kinetic energy is computed as 1/2 I w^2, where I is the
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inertia tensor for the aspherical particle and w is its angular
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velocity, which is computed from its angular momentum.
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</P>
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2008-03-19 05:02:30 +08:00
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<P>IMPORTANT NOTE: For <A HREF = "dimension.html">2d models</A>, particles are treated
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2008-03-19 04:39:07 +08:00
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as ellipsoids, not ellipses, meaning their moments of inertia will be
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the same as in 3d.
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2008-03-18 08:23:39 +08:00
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</P>
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<P>A 6-component kinetic energy tensor is also calculated by this
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compute. The formula for the components of the tensor is the same as
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the above formula, except that v^2 and w^2 are replaced by vx*vy and
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wx*wy for the xy component, and the appropriate elements of the
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inertia tensor are used.
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</P>
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<P>The number of atoms contributing to the temperature is assumed to be
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constant for the duration of the run; use the <I>dynamic</I> option of the
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<A HREF = "compute_modify.html">compute_modify</A> command if this is not the case.
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</P>
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<P>This compute subtracts out translational degrees-of-freedom due to
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fixes that constrain molecular motion, such as <A HREF = "fix_shake.html">fix
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shake</A> and <A HREF = "fix_rigid.html">fix rigid</A>. This means the
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temperature of groups of atoms that include these constraints will be
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computed correctly. If needed, the subtracted degrees-of-freedom can
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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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2007-04-20 07:25:27 +08:00
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</P>
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2008-01-03 03:25:15 +08:00
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<P><B>Output info:</B>
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</P>
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<P>The scalar value calculated by this compute is "intensive", meaning it
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is independent of the number of atoms in the simulation. The vector
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values are "extensive", meaning they scale with the number of atoms in
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the simulation.
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</P>
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2007-04-20 07:25:27 +08:00
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<P><B>Restrictions:</B>
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</P>
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2008-03-18 08:23:39 +08:00
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<P>This compute requires that particles be represented as extended
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ellipsoids and not point particles. This means they will have an
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angular momentum and a shape which is determined by the
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<A HREF = "shape.html">shape</A> command.
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2007-04-20 07:25:27 +08:00
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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>
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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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