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compute_ke.txt
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.. index:: compute ke
compute ke command
==================
Syntax
""""""
.. parsed-literal::
compute ID group-ID ke
* ID, group-ID are documented in :doc:`compute <compute>` command
* ke = style name of this compute command
Examples
""""""""
.. parsed-literal::
compute 1 all ke
Description
"""""""""""
Define a computation that calculates the translational kinetic energy
of a group of particles.
The kinetic energy of each particle is computed as 1/2 m v^2, where m
and v are the mass and velocity of the particle.
There is a subtle difference between the quantity calculated by this
compute and the kinetic energy calculated by the *ke* or *etotal*
keyword used in thermodynamic output, as specified by the
:doc:`thermo_style <thermo_style>` command. For this compute, kinetic
energy is "translational" kinetic energy, calculated by the simple
formula above. For thermodynamic output, the *ke* keyword infers
kinetic energy from the temperature of the system with 1/2 Kb T of
energy for each degree of freedom. For the default temperature
computation via the :doc:`compute temp <compute_temp>` command, these
are the same. But different computes that calculate temperature can
subtract out different non-thermal components of velocity and/or
include different degrees of freedom (translational, rotational, etc).
**Output info:**
This compute calculates a global scalar (the summed KE). This value
can be used by any command that uses a global scalar value from a
compute as input. See :ref:`Section_howto 15 <howto_15>`
for an overview of LAMMPS output options.
The scalar value calculated by this compute is "extensive". The
scalar value will be in energy :doc:`units <units>`.
Restrictions
""""""""""""
none
Related commands
""""""""""""""""
:doc:`compute erotate/sphere <compute_erotate_sphere>`
**Default:** none
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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