98 lines
3.5 KiB
Plaintext
98 lines
3.5 KiB
Plaintext
.. index:: fix_modify
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fix_modify command
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==================
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Syntax
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""""""
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.. parsed-literal::
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fix_modify fix-ID keyword value ...
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* fix-ID = ID of the fix to modify
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* one or more keyword/value pairs may be appended
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* keyword = *temp* or *press* or *energy* or *respa*
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.. parsed-literal::
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*temp* value = compute ID that calculates a temperature
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*press* value = compute ID that calculates a pressure
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*energy* value = *yes* or *no*
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*respa* value = *1* to *max respa level* or *0* (= outmost level)
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Examples
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""""""""
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.. parsed-literal::
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fix_modify 3 temp myTemp press myPress
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fix_modify 1 energy yes
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fix_modify tether respa 2
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Description
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"""""""""""
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Modify one or more parameters of a previously defined fix. Only
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specific fix styles support specific parameters. See the doc pages
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for individual fix commands for info on which ones support which
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fix_modify parameters.
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The *temp* keyword is used to determine how a fix computes
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temperature. The specified compute ID must have been previously
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defined by the user via the :doc:`compute <compute>` command and it must
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be a style of compute that calculates a temperature. All fixes that
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compute temperatures define their own compute by default, as described
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in their documentation. Thus this option allows the user to override
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the default method for computing T.
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The *press* keyword is used to determine how a fix computes pressure.
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The specified compute ID must have been previously defined by the user
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via the :doc:`compute <compute>` command and it must be a style of
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compute that calculates a pressure. All fixes that compute pressures
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define their own compute by default, as described in their
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documentation. Thus this option allows the user to override the
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default method for computing P.
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For fixes that calculate a contribution to the potential energy of the
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system, the *energy* keyword will include that contribution in
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thermodynamic output of potential energy. See the
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:doc:`thermo_style <thermo_style>` command for info on how potential
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energy is output. The contribution by itself can be printed by using
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the keyword f_ID in the thermo_style custom command, where ID is the
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fix-ID of the appropriate fix. Note that you must use this setting
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for a fix if you are using it when performing an :doc:`energy minimization <minimize>` and if you want the energy and forces it
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produces to be part of the optimization criteria.
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For fixes that set or modify forces, it may be possible to select at
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which :doc:`r-RESPA <run_style>` level the fix operates via the *respa*
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keyword. The RESPA level at which the fix is active can be selected.
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This is a number ranging from 1 to the number of levels. If the RESPA
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level is larger than the current maximum, the outermost level will be
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used, which is also the default setting. This default can be restored
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using a value of *0* for the RESPA level. The affected fix has to be
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programmed to support this feature; if not, *fix_modify* will report
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an error. Active fixes with a custom RESPA level setting are reported
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with their specified level at the beginning of a r-RESPA run.
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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:`fix <fix>`, :doc:`compute temp <compute_temp>`, :doc:`compute pressure <compute_pressure>`, :doc:`thermo_style <thermo_style>`
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Default
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"""""""
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The option defaults are temp = ID defined by fix, press = ID defined
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by fix, energy = no, respa = 0.
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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