94 lines
2.8 KiB
ReStructuredText
94 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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.. code-block:: LAMMPS
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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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.. code-block:: LAMMPS
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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 :math:`\frac{1}{2} m
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v^2` and the kinetic energy for each electron is computed as
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:math:`\frac{1}{2}(m_e v^2 + \frac{3}{4} m_e s^2)`, where :math:`m`
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corresponds to the nuclear mass, :math:`m_e` to the electron mass, :math:`v`
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to the translational velocity of each particle, and :math:`s` to the radial
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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 :math:`\frac{1}{2} k_B T` of energy for each degree of
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freedom. For the eFF temperature computation via the :doc:`compute
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temp_eff <compute_temp_eff>` command, these are the same. But
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different computes that calculate temperature can subtract out different
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non-thermal components of velocity and/or include other degrees of
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freedom.
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.. warning::
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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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.. code-block:: LAMMPS
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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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"""""""""""
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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>` 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 EFF package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package <Build_package>` page for more info.
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Related commands
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""""""""""""""""
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none
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Default
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"""""""
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none
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