81 lines
2.4 KiB
ReStructuredText
81 lines
2.4 KiB
ReStructuredText
.. index:: compute pressure/alchemy
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compute pressure/alchemy 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 pressure/alchemy fix-ID
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* pressure/alchemy = style name of this compute command
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* fix-ID = ID of :doc:`fix alchemy <fix_alchemy>` command
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Examples
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""""""""
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.. code-block:: LAMMPS
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fix trans all alchemy
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compute mixed all pressure/alchemy trans
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thermo_modify press mixed
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Description
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"""""""""""
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.. versionadded:: TBD
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Define a compute style that makes the "mixed" system pressure available
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for a system that uses the :doc:`fix alchemy <fix_alchemy>` command to
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transform one topology to another. This can be used in combination with
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either :doc:`thermo_modify press <thermo_modify>` or :doc:`fix_modify
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press <fix_modify>` to output and access a pressure consistent with the
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simulated combined two topology system.
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The actual pressure is determined with :doc:`compute pressure
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<compute_pressure>` commands that are internally used by :doc:`fix
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alchemy <fix_alchemy>` for each topology individually and then combined.
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This command just extracts the information from the fix.
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The ``examples/PACKAGES/alchemy`` folder contains an example input for this command.
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----------
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Output info
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"""""""""""
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This compute calculates a global scalar (the pressure) and a global
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vector of length 6 (the pressure tensor), which can be accessed by
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indices 1--6. These values can be used by any command that uses global
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scalar or vector values from a compute as input. See the :doc:`Howto
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output <Howto_output>` page for an overview of LAMMPS output options.
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The ordering of values in the symmetric pressure tensor is as follows:
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:math:`p_{xx},` :math:`p_{yy},` :math:`p_{zz},` :math:`p_{xy},`
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:math:`p_{xz},` :math:`p_{yz}.`
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The scalar and vector values calculated by this compute are "intensive".
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The scalar and vector values will be in pressure :doc:`units <units>`.
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Restrictions
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""""""""""""
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This compute is part of the REPLICA package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package
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<Build_package>` page for more info.
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Related commands
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""""""""""""""""
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:doc:`fix alchemy <fix_alchemy>`, :doc:`compute pressure <compute_pressure>`,
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:doc:`thermo_modify <thermo_modify>`, :doc:`fix_modify <fix_modify>`
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Default
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"""""""
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none
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