.. index:: bond_style harmonic/shift
.. index:: bond_style harmonic/shift/omp

bond_style harmonic/shift command
=================================

Accelerator Variants: *harmonic/shift/omp*

Syntax
""""""

.. code-block:: LAMMPS

   bond_style harmonic/shift

Examples
""""""""

.. code-block:: LAMMPS

   bond_style harmonic/shift
   bond_coeff 5 10.0 0.5 1.0

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

The *harmonic/shift* bond style is a shifted harmonic bond that uses
the potential

.. math::

   E = \frac{U_{\text{min}}}{(r_0-r_c)^2} \left[ (r-r_0)^2-(r_c-r_0)^2 \right]

where :math:`r_0` is the equilibrium bond distance, and :math:`r_c` the
critical distance.  The potential energy has the value
:math:`-U_{\text{min}}` at :math:`r_0` and zero at :math:`r_c`.  This
bond style differs from :doc:`bond_style harmonic <bond_harmonic>`
by the value of the potential energy.

The equivalent spring constant value *K* for use with :doc:`bond_style
harmonic <bond_harmonic>` can be computed using :math:`K =
U_{\text{min}} / [(r_0-r_c)^2]`.

The following coefficients must be defined for each bond type via the
:doc:`bond_coeff <bond_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:`U_{\text{min}}` (energy)
* :math:`r_0` (distance)
* :math:`r_c` (distance)

----------

.. include:: accel_styles.rst

----------

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

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

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

:doc:`bond_coeff <bond_coeff>`, :doc:`delete_bonds <delete_bonds>`,
:doc:`bond style harmonic <bond_harmonic>`,
:doc:`bond style harmonic/shift/cut <bond_harmonic_shift_cut>`

Default
"""""""

none