71 lines
1.9 KiB
ReStructuredText
71 lines
1.9 KiB
ReStructuredText
.. index:: compute ke
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compute ke command
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==================
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Syntax
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""""""
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.. code-block:: LAMMPS
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compute ID group-ID ke
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* ke = style name of this compute command
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all ke
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Description
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"""""""""""
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Define a computation that calculates the translational kinetic energy
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of a group of particles.
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The kinetic energy of each particle is computed as :math:`\frac{1}{2} m
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v^2`, where *m* and *v* are the mass and velocity of the particle,
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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" kinetic energy, calculated by the simple
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formula above. For thermodynamic output, the *ke* keyword infers
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kinetic energy from the temperature of the system with
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:math:`\frac{1}{2} k_B T` of energy for each degree of freedom. For the
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default temperature computation via the :doc:`compute temp
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<compute_temp>` command, these are the same.
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However, different computes that calculate temperature can subtract out
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different non-thermal components of velocity and/or include different degrees
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of freedom (translational, rotational, etc.).
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Output info
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"""""""""""
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This compute calculates a global scalar (the summed KE). This value
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can be used by any command that uses a global scalar value from a
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compute as input. See the :doc:`Howto output <Howto_output>` doc page
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for an 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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none
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Related commands
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""""""""""""""""
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:doc:`compute erotate/sphere <compute_erotate_sphere>`
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Default
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"""""""
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none
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