forked from lijiext/lammps
104 lines
3.0 KiB
Plaintext
104 lines
3.0 KiB
Plaintext
.. index:: angle_style cosine/shift/exp
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angle_style cosine/shift/exp command
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====================================
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angle_style cosine/shift/exp/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 cosine/shift/exp
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Examples
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""""""""
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.. parsed-literal::
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angle_style cosine/shift/exp
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angle_coeff * 10.0 45.0 2.0
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Description
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"""""""""""
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The *cosine/shift/exp* angle style uses the potential
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.. image:: Eqs/angle_cosine_shift_exp.jpg
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:align: center
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where Umin, theta, and a are defined for each angle type.
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The potential is bounded between [-Umin:0] and the minimum is
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located at the angle theta0. The a parameter can be both positive or
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negative and is used to control the spring constant at the
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equilibrium.
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The spring constant is given by k = A exp(A) Umin / [2 (Exp(a)-1)].
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For a > 3, k/Umin = a/2 to better than 5% relative error. For negative
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values of the a parameter, the spring constant is essentially zero,
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and anharmonic terms takes over. The potential is furthermore well
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behaved in the limit a -> 0, where it has been implemented to linear
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order in a for a < 0.001. In this limit the potential reduces to the
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cosineshifted potential.
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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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* umin (energy)
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* theta (angle)
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* A (real number)
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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
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USER-MISC package. See the :ref:`Making LAMMPS <start_3>`
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section 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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:doc:`angle_cosine_shift <angle_cosine_shift>`,
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:doc:`dihedral_cosine_shift_exp <dihedral_cosine_shift_exp>`
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**Default:** none
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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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