84 lines
2.8 KiB
ReStructuredText
84 lines
2.8 KiB
ReStructuredText
.. index:: compute_modify
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compute_modify 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_modify compute-ID keyword value ...
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* compute-ID = ID of the compute to modify
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* one or more keyword/value pairs may be listed
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* keyword = *extra/dof* or *extra* or *dynamic/dof* or *dynamic*
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.. parsed-literal::
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*extra/dof* value = N
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N = # of extra degrees of freedom to subtract
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*extra* syntax is identical to *extra/dof*, will be disabled at some point
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*dynamic/dof* value = *yes* or *no*
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yes/no = do or do not re-compute the number of degrees of freedom (DOF) contributing to the temperature
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*dynamic* syntax is identical to *dynamic/dof*, will be disabled at some point
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute_modify myTemp extra/dof 0
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compute_modify newtemp dynamic/dof yes extra/dof 600
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Description
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"""""""""""
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Modify one or more parameters of a previously defined compute. Not
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all compute styles support all parameters.
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The *extra/dof* or *extra* keyword refers to how many degrees of
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freedom are subtracted (typically from :math:`3N`) as a normalizing
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factor in a temperature computation. Only computes that compute a
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temperature use this option. The default is 2 or 3 for :doc:`2d or 3d
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systems <dimension>` which is a correction factor for an ensemble of
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velocities with zero total linear momentum. For compute temp/partial,
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if one or more velocity components are excluded, the value used for
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*extra* is scaled accordingly. You can use a negative number for the
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*extra* parameter if you need to add degrees-of-freedom. See the
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:doc:`compute temp/asphere <compute_temp_asphere>` command for an
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example.
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The *dynamic/dof* or *dynamic* keyword determines whether the number
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of atoms :math:`N` in the compute group and their associated degrees
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of freedom (DOF) are re-computed each time a temperature is computed.
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Only compute styles that calculate a temperature use this option. By
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default, :math:`N` and their DOF are assumed to be constant. If you
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are adding atoms or molecules to the system (see the :doc:`fix pour
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<fix_pour>`, :doc:`fix deposit <fix_deposit>`, and :doc:`fix gcmc
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<fix_gcmc>` commands) or expect atoms or molecules to be lost
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(e.g. due to exiting the simulation box or via :doc:`fix evaporate
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<fix_evaporate>`), then this option should be used to ensure the
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temperature is correctly normalized.
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.. note::
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The *extra* and *dynamic* keywords should not be used as they
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are deprecated (March 2017) and will eventually be disabled. Instead,
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use the equivalent *extra/dof* and *dynamic/dof* keywords.
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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 <compute>`
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Default
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"""""""
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The option defaults are extra/dof = 2 or 3 for 2d or 3d systems and
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dynamic/dof = *no*.
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