forked from lijiext/lammps
140 lines
3.7 KiB
Plaintext
140 lines
3.7 KiB
Plaintext
.. index:: angle_style class2
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angle_style class2 command
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==========================
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angle_style class2/omp command
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==============================
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Syntax
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""""""
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.. parsed-literal::
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angle_style class2
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Examples
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""""""""
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.. parsed-literal::
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angle_style class2
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angle_coeff * 75.0
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angle_coeff 1 bb 10.5872 1.0119 1.5228
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angle_coeff * ba 3.6551 24.895 1.0119 1.5228
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Description
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"""""""""""
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The *class2* angle style uses the potential
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.. image:: Eqs/angle_class2.jpg
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:align: center
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where Ea is the angle term, Ebb is a bond-bond term, and Eba is a
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bond-angle term. Theta0 is the equilibrium angle and r1 and r2 are
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the equilibrium bond lengths.
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See :ref:`(Sun) <angle-Sun>` for a description of the COMPASS class2 force field.
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Coefficients for the Ea, Ebb, and Eba formulas must be defined for
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each angle type via the :doc:`angle_coeff <angle_coeff>` command as in
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the example above, or in the data file or restart files read by the
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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands.
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These are the 4 coefficients for the Ea formula:
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* theta0 (degrees)
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* K2 (energy/radian^2)
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* K3 (energy/radian^3)
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* K4 (energy/radian^4)
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Theta0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of the various K are in per-radian.
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For the Ebb formula, each line in a :doc:`angle_coeff <angle_coeff>`
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command in the input script lists 4 coefficients, the first of which
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is "bb" to indicate they are BondBond coefficients. In a data file,
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these coefficients should be listed under a "BondBond Coeffs" heading
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and you must leave out the "bb", i.e. only list 3 coefficients after
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the angle type.
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* bb
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* M (energy/distance^2)
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* r1 (distance)
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* r2 (distance)
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For the Eba formula, each line in a :doc:`angle_coeff <angle_coeff>`
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command in the input script lists 5 coefficients, the first of which
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is "ba" to indicate they are BondAngle coefficients. In a data file,
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these coefficients should be listed under a "BondAngle Coeffs" heading
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and you must leave out the "ba", i.e. only list 4 coefficients after
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the angle type.
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* ba
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* N1 (energy/distance^2)
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* N2 (energy/distance^2)
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* r1 (distance)
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* r2 (distance)
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The theta0 value in the Eba formula is not specified, since it is the
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same value from the Ea formula.
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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Restrictions
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""""""""""""
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This angle style can only be used if LAMMPS was built with the CLASS2
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package. See the :ref:`Making LAMMPS <start_3>` section
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for more info on packages.
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Related commands
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""""""""""""""""
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:doc:`angle_coeff <angle_coeff>`
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**Default:** none
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----------
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.. _angle-Sun:
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**(Sun)** Sun, J Phys Chem B 102, 7338-7364 (1998).
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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