git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14950 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/html/_sources/compute_pe.txt

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+.. index:: compute pe
+
+compute pe command
+==================
+
+compute pe/cuda command
+=======================
+
+Syntax
+""""""
+
+.. parsed-literal::
+
+   compute ID group-ID pe keyword ...
+
+* ID, group-ID are documented in :doc:`compute <compute>` command
+* pe = style name of this compute command
+* zero or more keywords may be appended
+* keyword = *pair* or *bond* or *angle* or *dihedral* or *improper* or *kspace*
+
+Examples
+""""""""
+
+.. parsed-literal::
+
+   compute 1 all pe
+   compute molPE all pe bond angle dihedral improper
+
+Description
+"""""""""""
+
+Define a computation that calculates the potential energy of the
+entire system of atoms.  The specified group must be "all".  See the
+:doc:`compute pe/atom <compute_pe_atom>` command if you want per-atom
+energies.  These per-atom values could be summed for a group of atoms
+via the :doc:`compute reduce <compute_reduce>` command.
+
+The energy is calculated by the various pair, bond, etc potentials
+defined for the simulation.  If no extra keywords are listed, then the
+potential energy is the sum of pair, bond, angle, dihedral, improper,
+and kspace (long-range) energy.  If any extra keywords are listed,
+then only those components are summed to compute the potential energy.
+
+The Kspace contribution requires 1 extra FFT each timestep the energy
+is calculated, if using the PPPM solver via the :doc:`kspace_style pppm <kspace_style>` command.  Thus it can increase the cost of the
+PPPM calculation if it is needed on a large fraction of the simulation
+timesteps.
+
+Various fixes can contribute to the total potential energy of the
+system.  See the doc pages for :doc:`individual fixes <fix>` for
+details.  The *thermo* option of the
+:doc:`compute_modify <compute_modify>` command determines whether these
+contributions are added into the computed potential energy.  If no
+keywords are specified the default is *yes*\ .  If any keywords are
+specified, the default is *no*\ .
+
+A compute of this style with the ID of "thermo_pe" is created when
+LAMMPS starts up, as if this command were in the input script:
+
+.. parsed-literal::
+
+   compute thermo_pe all pe
+
+See the "thermo_style" command for more details.
+
+
+----------
+
+
+Styles with a *cuda*\ , *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
+functionally the same as the corresponding style without the suffix.
+They have been optimized to run faster, depending on your available
+hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
+of the manual.  The accelerated styles take the same arguments and
+should produce the same results, except for round-off and precision
+issues.
+
+These accelerated styles are part of the USER-CUDA, GPU, USER-INTEL,
+KOKKOS, USER-OMP and OPT packages, respectively.  They are only
+enabled if LAMMPS was built with those packages.  See the :ref:`Making LAMMPS <start_3>` section for more info.
+
+You can specify the accelerated styles explicitly in your input script
+by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
+use the :doc:`suffix <suffix>` command in your input script.
+
+See :doc:`Section_accelerate <Section_accelerate>` of the manual for
+more instructions on how to use the accelerated styles effectively.
+
+
+----------
+
+
+**Output info:**
+
+This compute calculates a global scalar (the potential energy).  This
+value can be used by any command that uses a global scalar value from
+a compute as input.  See :ref:`Section_howto 15 <howto_15>` for an overview of LAMMPS output
+options.
+
+The scalar value calculated by this compute is "extensive".  The
+scalar value will be in energy :doc:`units <units>`.
+
+Restrictions
+""""""""""""
+ none
+
+Related commands
+""""""""""""""""
+
+:doc:`compute pe/atom <compute_pe_atom>`
+
+**Default:** none
+
+
+.. _lws: http://lammps.sandia.gov
+.. _ld: Manual.html
+.. _lc: Section_commands.html#comm