forked from lijiext/lammps
126 lines
4.2 KiB
Plaintext
126 lines
4.2 KiB
Plaintext
.. index:: compute temp
|
|
|
|
compute temp command
|
|
====================
|
|
|
|
compute temp/kk command
|
|
=======================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
compute ID group-ID temp
|
|
|
|
* ID, group-ID are documented in :doc:`compute <compute>` command
|
|
* temp = style name of this compute command
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. parsed-literal::
|
|
|
|
compute 1 all temp
|
|
compute myTemp mobile temp
|
|
|
|
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. :doc:`thermo_modify <thermo_modify>`, :doc:`fix temp/rescale <fix_temp_rescale>`, :doc:`fix npt <fix_nh>`, 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
|
|
:doc:`compute_modify <compute_modify>` command if this is not the case.
|
|
|
|
This compute subtracts out degrees-of-freedom due to fixes that
|
|
constrain molecular motion, such as :doc:`fix shake <fix_shake>` and
|
|
:doc:`fix rigid <fix_rigid>`. 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 :doc:`compute_modify <compute_modify>` 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:
|
|
|
|
.. parsed-literal::
|
|
|
|
compute thermo_temp all temp
|
|
|
|
See the "thermo_style" command for more details.
|
|
|
|
See :ref:`this howto section <howto_16>` of the manual for
|
|
a discussion of different ways to compute temperature and perform
|
|
thermostatting.
|
|
|
|
|
|
----------
|
|
|
|
|
|
Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* 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 :doc:`Section_accelerate <Section_accelerate>`
|
|
of the manual. The accelerated styles take the same arguments and
|
|
should produce the same results, except for round-off and precision
|
|
issues.
|
|
|
|
These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
|
|
USER-OMP and OPT packages, respectively. They are only enabled if
|
|
LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
|
|
|
|
You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
|
|
use the :doc:`suffix <suffix>` command in your input script.
|
|
|
|
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
|
|
more instructions on how to use the accelerated styles effectively.
|
|
|
|
|
|
----------
|
|
|
|
|
|
**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 :ref:`this section <howto_15>` for an overview of LAMMPS output
|
|
options.
|
|
|
|
The scalar value calculated by this compute is "intensive". The
|
|
vector values are "extensive".
|
|
|
|
The scalar value will be in temperature :doc:`units <units>`. The
|
|
vector values will be in energy :doc:`units <units>`.
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
none
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`compute temp/partial <compute_temp_partial>`, :doc:`compute temp/region <compute_temp_region>`, :doc:`compute pressure <compute_pressure>`
|
|
|
|
**Default:** none
|
|
|
|
|
|
.. _lws: http://lammps.sandia.gov
|
|
.. _ld: Manual.html
|
|
.. _lc: Section_commands.html#comm
|