lammps/doc/compute_temp.txt

"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

compute temp command :h3

[Syntax:]

compute ID group-ID temp :pre

ID, group-ID are documented in "compute"_compute.html command
temp = style name of this compute command :ul

[Examples:]

compute 1 all temp
compute myTemp mobile temp :pre

[Description:]

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. "thermo_modify"_thermo_modify.html, "fix
temp/rescale"_fix_temp_rescale.html, "fix npt"_fix_npt.html, etc.

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.

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.

The number of atoms contributing to the temperature is assumed to be
constant for the duration of the run; use the {dynamic} option of the
"compute_modify"_compute_modify.html command if this is not the case.

This compute subtracts out degrees-of-freedom due to fixes that
constrain molecular motion, such as "fix shake"_fix_shake.html and
"fix rigid"_fix_rigid.html.  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
{extra} option of the "compute_modify"_compute_modify.html command.

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:

compute thermo_temp all temp :pre

See the "thermo_style" command for more details.

See "this howto section"_Section_howto.html#4_16 of the manual for a
discussion of different ways to compute temperature and perform
thermostatting.

[Output info:]

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 "this
section"_Section_howto.html#4_15 for an overview of LAMMPS output
options.

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.

[Restrictions:] none

[Related commands:]

"compute temp/partial"_compute_temp_partial.html, "compute
temp/region"_compute_temp_region.html, "compute
pressure"_compute_pressure.html

[Default:] none