forked from lijiext/lammps
92 lines
2.7 KiB
Plaintext
92 lines
2.7 KiB
Plaintext
.. index:: compute pe
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compute pe 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 pe keyword ...
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* pe = style name of this compute command
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* zero or more keywords may be appended
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* keyword = *pair* or *bond* or *angle* or *dihedral* or *improper* or *kspace*
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Examples
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""""""""
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.. parsed-literal::
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compute 1 all pe
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compute molPE all pe bond angle dihedral improper
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Description
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"""""""""""
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Define a computation that calculates the potential energy of the
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entire system of atoms. The specified group must be "all". See the
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:doc:`compute pe/atom <compute_pe_atom>` command if you want per-atom
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energies. These per-atom values could be summed for a group of atoms
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via the :doc:`compute reduce <compute_reduce>` command.
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The energy is calculated by the various pair, bond, etc potentials
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defined for the simulation. If no extra keywords are listed, then the
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potential energy is the sum of pair, bond, angle, dihedral, improper,
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and kspace (long-range) energy. If any extra keywords are listed,
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then only those components are summed to compute the potential energy.
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The Kspace contribution requires 1 extra FFT each timestep the energy
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is calculated, if using the PPPM solver via the :doc:`kspace_style pppm <kspace_style>` command. Thus it can increase the cost of the
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PPPM calculation if it is needed on a large fraction of the simulation
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timesteps.
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Various fixes can contribute to the total potential energy of the
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system. See the doc pages for :doc:`individual fixes <fix>` for
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details. The *thermo* option of the
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:doc:`compute_modify <compute_modify>` command determines whether these
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contributions are added into the computed potential energy. If no
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keywords are specified the default is *yes*\ . If any keywords are
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specified, the default is *no*\ .
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A compute of this style with the ID of "thermo_pe" is created when
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LAMMPS starts up, as if this command were in the input script:
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.. parsed-literal::
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compute thermo_pe all pe
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See the "thermo_style" command for more details.
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----------
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**Output info:**
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This compute calculates a global scalar (the potential energy). This
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value can be used by any command that uses a global scalar value from
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a compute as input. See :ref:`Section_howto 15 <howto_15>` for an overview of LAMMPS output
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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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none
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Related commands
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""""""""""""""""
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:doc:`compute pe/atom <compute_pe_atom>`
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**Default:** none
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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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