91 lines
2.8 KiB
ReStructuredText
91 lines
2.8 KiB
ReStructuredText
.. index:: compute ke/eff
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compute ke/eff command
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======================
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Syntax
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""""""
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.. parsed-literal::
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compute ID group-ID ke/eff
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* ke/eff = style name of this compute command
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Examples
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""""""""
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.. parsed-literal::
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compute 1 all ke/eff
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Description
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"""""""""""
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Define a computation that calculates the kinetic energy of motion of a
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group of eFF particles (nuclei and electrons), as modeled with the
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:doc:`electronic force field <pair_eff>`.
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The kinetic energy for each nucleus is computed as 1/2 m v\^2 and the
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kinetic energy for each electron is computed as 1/2(me v\^2 + 3/4 me
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s\^2), where m corresponds to the nuclear mass, me to the electron
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mass, v to the translational velocity of each particle, and s to the
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radial velocity of the electron, respectively.
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There is a subtle difference between the quantity calculated by this
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compute and the kinetic energy calculated by the *ke* or *etotal*
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keyword used in thermodynamic output, as specified by the
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:doc:`thermo\_style <thermo_style>` command. For this compute, kinetic
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energy is "translational" and "radial" (only for electrons) kinetic
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energy, calculated by the simple formula above. For thermodynamic
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output, the *ke* keyword infers kinetic energy from the temperature of
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the system with 1/2 Kb T of energy for each degree of freedom. For
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the eFF temperature computation via the :doc:`compute temp\_eff <compute_temp_eff>` command, these are the same. But
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different computes that calculate temperature can subtract out
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different non-thermal components of velocity and/or include other
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degrees of freedom.
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IMPRORTANT NOTE: The temperature in eFF models should be monitored via
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the :doc:`compute temp/eff <compute_temp_eff>` command, which can be
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printed with thermodynamic output by using the
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:doc:`thermo\_modify <thermo_modify>` command, as shown in the following
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example:
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.. parsed-literal::
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compute effTemp all temp/eff
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thermo_style custom step etotal pe ke temp press
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thermo_modify temp effTemp
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See :doc:`compute temp/eff <compute_temp_eff>`.
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**Output info:**
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This compute calculates a global scalar (the KE). This value can be
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used by any command that uses a global scalar value from a compute as
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input. See the :doc:`Howto output <Howto_output>` doc page for an
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overview of LAMMPS output options.
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The scalar value calculated by this compute is "extensive". The
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scalar value will be in energy :doc:`units <units>`.
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Restrictions
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""""""""""""
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This compute is part of the USER-EFF package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package <Build_package>` doc page for more info.
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**Related commands:** none
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Commands_all.html
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