.. index:: dihedral_style quadratic

dihedral_style quadratic command
================================

dihedral_style quadratic/omp command
====================================

Syntax
""""""

.. code-block:: LAMMPS

   dihedral_style quadratic

Examples
""""""""

.. code-block:: LAMMPS

   dihedral_style quadratic
   dihedral_coeff 100.0 80.0

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

The *quadratic* dihedral style uses the potential:

.. math::

   E = K (\phi - \phi_0)^2

This dihedral potential can be used to keep a dihedral in a predefined
value (cis=zero, right-hand convention is used).

The following coefficients must be defined for each dihedral type via
the :doc:`dihedral_coeff <dihedral_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:

* :math:`K` (energy/radian\^2)
* :math:`\phi_0` (degrees)

----------

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 on the :doc:`Speed packages <Speed_packages>` doc
page.  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 :doc:`Build package <Build_package>` doc page for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
:doc:`suffix <suffix>` command in your input script.

See the :doc:`Speed packages <Speed_packages>` doc page for more
instructions on how to use the accelerated styles effectively.

----------

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

This angle style can only be used if LAMMPS was built with the
USER_MISC package.  See the :doc:`Build package <Build_package>` doc
page for more info.

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

:doc:`dihedral_coeff <dihedral_coeff>`

**Default:** none
