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bond_fene_expand.txt
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.. index:: bond_style fene/expand
bond_style fene/expand command
==============================
bond_style fene/expand/omp command
==================================
Syntax
""""""
.. parsed-literal::
bond_style fene/expand
Examples
""""""""
.. parsed-literal::
bond_style fene/expand
bond_coeff 1 30.0 1.5 1.0 1.0 0.5
Description
"""""""""""
The *fene/expand* bond style uses the potential
.. image:: Eqs/bond_fene_expand.jpg
:align: center
to define a finite extensible nonlinear elastic (FENE) potential
:ref:`(Kremer) <Kremer>`, used for bead-spring polymer models. The first
term is attractive, the 2nd Lennard-Jones term is repulsive.
The *fene/expand* bond style is similar to *fene* except that an extra
shift factor of delta (positive or negative) is added to *r* to
effectively change the bead size of the bonded atoms. The first term
now extends to R0 + delta and the 2nd term is cutoff at 2^(1/6) sigma
+ delta.
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:
* K (energy/distance^2)
* R0 (distance)
* epsilon (energy)
* sigma (distance)
* delta (distance)
----------
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.
----------
Restrictions
""""""""""""
This bond 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.
You typically should specify `special_bonds fene <special_bonds.html">`_
or :doc:`special_bonds lj/coul 0 1 1 <special_bonds>` to use this bond
style. LAMMPS will issue a warning it that's not the case.
Related commands
""""""""""""""""
:doc:`bond_coeff <bond_coeff>`, :doc:`delete_bonds <delete_bonds>`
**Default:** none
----------
.. _Kremer:
**(Kremer)** Kremer, Grest, J Chem Phys, 92, 5057 (1990).
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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