69 lines
1.5 KiB
ReStructuredText
69 lines
1.5 KiB
ReStructuredText
.. index:: angle_style cosine/shift
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.. index:: angle_style cosine/shift/omp
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angle_style cosine/shift command
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================================
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Accelerator Variants: *cosine/shift/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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angle_style cosine/shift
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Examples
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""""""""
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.. code-block:: LAMMPS
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angle_style cosine/shift
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angle_coeff * 10.0 45.0
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Description
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"""""""""""
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The *cosine/shift* angle style uses the potential
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.. math::
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E = -\frac{U_{\text{min}}}{2} \left[ 1 + \cos(\theta-\theta_0) \right]
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where :math:`\theta_0` is the equilibrium angle. The potential is bounded
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between :math:`-U_{\text{min}}` and zero. In the neighborhood of the minimum
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:math:`E = - U_{\text{min}} + U_{\text{min}}/4(\theta - \theta_0)^2` hence
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the spring constant is :math:`\frac{U_{\text{min}}}{2}`.
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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:`U_{\text{min}}` (energy)
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* :math:`\theta` (angle)
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----------
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.. include:: accel_styles.rst
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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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EXTRA-MOLECULE 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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:doc:`angle_style cosine/shift/exp <angle_cosine_shift_exp>`
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Default
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"""""""
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none
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