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rLAMMPS lammps
compute_temp.html
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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>
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"
>
this section
</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_6"
>
-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"
>
this section
</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>
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