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lammps/doc/_sources/angle_class2.txt
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angle_class2.txt
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.. index:: angle_style class2
angle_style class2 command
==========================
angle_style class2/omp command
==============================
Syntax
""""""
.. parsed-literal::
angle_style class2
Examples
""""""""
.. parsed-literal::
angle_style class2
angle_coeff * 75.0
angle_coeff 1 bb 10.5872 1.0119 1.5228
angle_coeff * ba 3.6551 24.895 1.0119 1.5228
Description
"""""""""""
The *class2* angle style uses the potential
.. image:: Eqs/angle_class2.jpg
:align: center
where Ea is the angle term, Ebb is a bond-bond term, and Eba is a
bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are
the equilibrium bond lengths.
See :ref:`(Sun) <Sun>` for a description of the COMPASS class2 force field.
Coefficients for the Ea, Ebb, and Eba formulas must be defined for
each angle type via the :doc:`angle_coeff <angle_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.
These are the 4 coefficients for the Ea formula:
* theta0 (degrees)
* K2 (energy/radian^2)
* K3 (energy/radian^3)
* K4 (energy/radian^4)
Theta0 is specified in degrees, but LAMMPS converts it to radians
internally; hence the units of the various K are in per-radian.
For the Ebb formula, each line in a :doc:`angle_coeff <angle_coeff>`
command in the input script lists 4 coefficients, the first of which
is "bb" to indicate they are BondBond coefficients. In a data file,
these coefficients should be listed under a "BondBond Coeffs" heading
and you must leave out the "bb", i.e. only list 3 coefficients after
the angle type.
* bb
* M (energy/distance^2)
* r1 (distance)
* r2 (distance)
For the Eba formula, each line in a :doc:`angle_coeff <angle_coeff>`
command in the input script lists 5 coefficients, the first of which
is "ba" to indicate they are BondAngle coefficients. In a data file,
these coefficients should be listed under a "BondAngle Coeffs" heading
and you must leave out the "ba", i.e. only list 4 coefficients after
the angle type.
* ba
* N1 (energy/distance^2)
* N2 (energy/distance^2)
* r1 (distance)
* r2 (distance)
The theta0 value in the Eba formula is not specified, since it is the
same value from the Ea formula.
----------
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 angle style can only be used if LAMMPS was built with the CLASS2
package. See the :ref:`Making LAMMPS <start_3>` section
for more info on packages.
Related commands
""""""""""""""""
:doc:`angle_coeff <angle_coeff>`
**Default:** none
----------
.. _Sun:
**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998).
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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