.. index:: improper_style harmonic

improper_style harmonic command
===============================

improper_style harmonic/intel command
=====================================

improper_style harmonic/kk command
==================================

improper_style harmonic/omp command
===================================

Syntax
""""""

.. parsed-literal::

   improper_style harmonic

Examples
""""""""

.. parsed-literal::

   improper_style harmonic
   improper_coeff 1 100.0 0

Description
"""""""""""

The *harmonic* improper style uses the potential

.. image:: Eqs/improper_harmonic.jpg
   :align: center

where X is the improper angle, X0 is its equilibrium value, and K is a
prefactor.  Note that the usual 1/2 factor is included in K.

If the 4 atoms in an improper quadruplet (listed in the data file read
by the :doc:`read_data <read_data>` command) are ordered I,J,K,L then X
is the angle between the plane of I,J,K and the plane of J,K,L.
Alternatively, you can think of atoms J,K,L as being in a plane, and
atom I above the plane, and X as a measure of how far out-of-plane I
is with respect to the other 3 atoms.

Note that defining 4 atoms to interact in this way, does not mean that
bonds necessarily exist between I-J, J-K, or K-L, as they would in a
linear dihedral.  Normally, the bonds I-J, I-K, I-L would exist for an
improper to be defined between the 4 atoms.

The following coefficients must be defined for each improper type via
the :doc:`improper_coeff <improper_coeff>` command as in the example
above, or in the data file or restart files read by the
:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
commands:

* K (energy/radian^2)
* X0 (degrees)

X0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of K are in energy/radian^2.


----------


Styles with a *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 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.


----------


Restrictions
""""""""""""


This improper style can only be used if LAMMPS was built with the
MOLECULE package (which it is by default).  See the :ref:`Making LAMMPS <start_3>` section for more info on packages.

Related commands
""""""""""""""""

:doc:`improper_coeff <improper_coeff>`

**Default:** none


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm