forked from lijiext/lammps
96 lines
3.1 KiB
Plaintext
96 lines
3.1 KiB
Plaintext
.. index:: compute pair
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compute pair command
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====================
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Syntax
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""""""
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.. parsed-literal::
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compute ID group-ID pair pstyle evalue
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* pair = style name of this compute command
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* pstyle = style name of a pair style that calculates additional values
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* evalue = *epair* or *evdwl* or *ecoul* or blank (optional setting)
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Examples
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""""""""
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.. parsed-literal::
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compute 1 all pair gauss
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compute 1 all pair lj/cut/coul/cut ecoul
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compute 1 all pair reax
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Description
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"""""""""""
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Define a computation that extracts additional values calculated by a
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pair style, and makes them accessible for output or further processing
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by other commands. The group specified for this command is ignored.
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The specified *pstyle* must be a pair style used in your simulation
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either by itself or as a sub-style in a :doc:`pair_style hybrid or hybrid/overlay <pair_hybrid>` command.
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The *evalue* setting is optional; it may be left off the command. All
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pair styles tally a potential energy *epair* which may be broken into
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two parts: *evdwl* and *ecoul* such that *epair* = *evdwl* + *ecoul*.
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If the pair style calculates Coulombic interactions, their energy will
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be tallied in *ecoul*. Everything else (whether it is a Lennard-Jones
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style van der Waals interaction or not) is tallied in *evdwl*. If
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*evalue* is specified as *epair* or left out, then *epair* is stored
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as a global scalar by this compute. This is useful when using
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:doc:`pair_style hybrid <pair_hybrid>` if you want to know the portion
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of the total energy contributed by one sub-style. If *evalue* is
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specfied as *evdwl* or *ecoul*, then just that portion of the energy
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is stored as a global scalar.
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.. note::
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The energy returned by the *evdwl* keyword does not include tail
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corrections, even if they are enabled via the
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:doc:`pair_modify <pair_modify>` command.
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Some pair styles tally additional quantities, e.g. a breakdown of
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potential energy into a dozen or so components is tallied by the
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:doc:`pair_style reax <pair_reax>` commmand. These values (1 or more)
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are stored as a global vector by this compute. See the doc page for
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:doc:`individual pair styles <pair_style>` for info on these values.
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**Output info:**
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This compute calculates a global scalar which is *epair* or *evdwl* or
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*ecoul*. If the pair style supports it, it also calculates a global
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vector of length >= 1, as determined by the pair style. These values
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can be used by any command that uses global scalar or vector values
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from a compute as input. See :ref:`this section <howto_15>` for an overview of LAMMPS output
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options.
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The scalar and vector values calculated by this compute are
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"extensive".
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The scalar value will be in energy :doc:`units <units>`. The vector
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values will typically also be in energy :doc:`units <units>`, but see
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the doc page for the pair style for details.
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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 pe <compute_pe>`, :doc:`compute bond <compute_bond>`
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Default
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"""""""
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The default for *evalue* is *epair*.
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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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