92 lines
2.5 KiB
ReStructuredText
92 lines
2.5 KiB
ReStructuredText
.. index:: angle_style quartic
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angle_style quartic command
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===========================
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angle_style quartic/omp command
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===============================
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style quartic
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style quartic
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angle_coeff 1 129.1948 56.8726 -25.9442 -14.2221
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Description
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"""""""""""
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The *quartic* angle style uses the potential
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.. math::
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E = K_2 (\theta - \theta_0)^2 + K_3 (\theta - \theta_0)^3 + K_4 (\theta - \theta_0)^4
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where :math:`\theta_0` is the equilibrium value of the angle, and :math:`K` is a
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prefactor. Note that the usual 1/2 factor is included in :math:`K`.
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The following coefficients must be defined for each angle type via the
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:doc:`angle_coeff <angle_coeff>` command as in the example above, or in
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the data file or restart files read by the :doc:`read_data <read_data>`
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or :doc:`read_restart <read_restart>` commands:
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* :math:`\theta_0` (degrees)
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* :math:`K_2` (energy/radian\^2)
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* :math:`K_3` (energy/radian\^3)
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* :math:`K_4` (energy/radian\^4)
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:math:`\theta_0` is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of :math:`K` are in energy/radian\^2.
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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 on the :doc:`Speed packages <Speed_packages>` doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision 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 :doc:`Build package <Build_package>` doc page 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 :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
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:doc:`suffix <suffix>` command in your input script.
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See the :doc:`Speed packages <Speed_packages>` doc page for more
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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
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USER\_MISC package. See the :doc:`Build package <Build_package>` doc
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page for more info.
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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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