.. index:: compute ke/eff

compute ke/eff command
======================

Syntax
""""""

.. parsed-literal::

   compute ID group-ID ke/eff

* ID, group-ID are documented in :doc:`compute <compute>` command
* ke/eff = style name of this compute command

Examples
""""""""

.. parsed-literal::

   compute 1 all ke/eff

Description
"""""""""""

Define a computation that calculates the kinetic energy of motion of a
group of eFF particles (nuclei and electrons), as modeled with the
:doc:`electronic force field <pair_eff>`.

The kinetic energy for each nucleus is computed as 1/2 m v^2 and the
kinetic energy for each electron is computed as 1/2(me v^2 + 3/4 me
s^2), where m corresponds to the nuclear mass, me to the electron
mass, v to the translational velocity of each particle, and s to the
radial velocity of the electron, respectively.

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" and "radial" (only for electrons) 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 eFF temperature computation via the :doc:`compute temp_eff <compute_temp_eff>` command, these are the same.  But
different computes that calculate temperature can subtract out
different non-thermal components of velocity and/or include other
degrees of freedom.

IMPRORTANT NOTE: The temperature in eFF models should be monitored via
the :doc:`compute temp/eff <compute_temp_eff>` command, which can be
printed with thermodynamic output by using the
:doc:`thermo_modify <thermo_modify>` command, as shown in the following
example:

.. parsed-literal::

   compute         effTemp all temp/eff
   thermo_style    custom step etotal pe ke temp press 
   thermo_modify   temp effTemp

See :doc:`compute temp/eff <compute_temp_eff>`.

**Output info:**

This compute calculates a global scalar (the 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
""""""""""""


This compute is part of the USER-EFF package.  It is only enabled if
LAMMPS was built with that package.  See the :ref:`Making LAMMPS <start_3>` section for more info.

**Related commands:** none

**Default:** none


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm