forked from lijiext/lammps
118 lines
4.6 KiB
HTML
118 lines
4.6 KiB
HTML
<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>compute temp command
|
|
</H3>
|
|
<H3>compute temp/cuda command
|
|
</H3>
|
|
<P><B>Syntax:</B>
|
|
</P>
|
|
<PRE>compute ID group-ID temp
|
|
</PRE>
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
|
|
<LI>temp = style name of this compute command
|
|
</UL>
|
|
<P><B>Examples:</B>
|
|
</P>
|
|
<PRE>compute 1 all temp
|
|
compute myTemp mobile temp
|
|
</PRE>
|
|
<P><B>Description:</B>
|
|
</P>
|
|
<P>Define a computation that calculates the temperature of a group of
|
|
atoms. A compute of this style can be used by any command that
|
|
computes a temperature, e.g. <A HREF = "thermo_modify.html">thermo_modify</A>, <A HREF = "fix_temp_rescale.html">fix
|
|
temp/rescale</A>, <A HREF = "fix_nh.html">fix npt</A>, etc.
|
|
</P>
|
|
<P>The temperature is calculated by the formula KE = dim/2 N k T, where
|
|
KE = total kinetic energy of the group of atoms (sum of 1/2 m v^2),
|
|
dim = 2 or 3 = dimensionality of the simulation, N = number of atoms
|
|
in the group, k = Boltzmann constant, and T = temperature.
|
|
</P>
|
|
<P>A kinetic energy tensor, stored as a 6-element vector, is also
|
|
calculated by this compute for use in the computation of a pressure
|
|
tensor. The formula for the components of the tensor is the same as
|
|
the above formula, except that v^2 is replaced by vx*vy for the xy
|
|
component, etc. The 6 components of the vector are ordered xx, yy,
|
|
zz, xy, xz, yz.
|
|
</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>This compute subtracts out 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>A compute of this style with the ID of "thermo_temp" is created when
|
|
LAMMPS starts up, as if this command were in the input script:
|
|
</P>
|
|
<PRE>compute thermo_temp all temp
|
|
</PRE>
|
|
<P>See the "thermo_style" command for more details.
|
|
</P>
|
|
<P>See <A HREF = "Section_howto.html#howto_16">this howto section</A> of the manual for
|
|
a discussion of different ways to compute temperature and perform
|
|
thermostatting.
|
|
</P>
|
|
<HR>
|
|
|
|
<P>Styles with a <I>cuda</I> suffix are functionally the same as the
|
|
corresponding style without the suffix. They have been optimized to
|
|
run faster, depending on your available hardware, as discussed in
|
|
<A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual. The
|
|
accelerated styles take the same arguments and should produce the same
|
|
results, except for round-off and precision issues.
|
|
</P>
|
|
<P>These accelerated styles are part of the USER-CUDA package. They are
|
|
only enabled if LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
|
|
LAMMPS</A> section for more info.
|
|
</P>
|
|
<P>You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the <A HREF = "Section_start.html#start_7">-suffix command-line
|
|
switch</A> when you invoke LAMMPS, or you can
|
|
use the <A HREF = "suffix.html">suffix</A> command in your input script.
|
|
</P>
|
|
<P>See <A HREF = "Section_accelerate.html">Section_accelerate</A> of the manual for
|
|
more instructions on how to use the accelerated styles effectively.
|
|
</P>
|
|
<HR>
|
|
|
|
<P><B>Output info:</B>
|
|
</P>
|
|
<P>This compute calculates a global scalar (the temperature) and a global
|
|
vector of length 6 (KE tensor), which can be accessed by indices 1-6.
|
|
These values can be used by any command that uses global scalar or
|
|
vector values from a compute as input. See <A HREF = "Section_howto.html#howto_15">this
|
|
section</A> for an overview of LAMMPS output
|
|
options.
|
|
</P>
|
|
<P>The scalar value calculated by this compute is "intensive". The
|
|
vector are "extensive".
|
|
</P>
|
|
<P>The scalar value will be in temperature <A HREF = "units.html">units</A>. The
|
|
vector values will be in energy <A HREF = "units.html">units</A>.
|
|
</P>
|
|
<P><B>Restrictions:</B> none
|
|
</P>
|
|
<P><B>Related commands:</B>
|
|
</P>
|
|
<P><A HREF = "compute_temp_partial.html">compute temp/partial</A>, <A HREF = "compute_temp_region.html">compute
|
|
temp/region</A>, <A HREF = "compute_pressure.html">compute
|
|
pressure</A>
|
|
</P>
|
|
<P><B>Default:</B> none
|
|
</P>
|
|
</HTML>
|