86 lines
1.9 KiB
ReStructuredText
86 lines
1.9 KiB
ReStructuredText
.. index:: improper_style umbrella
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.. index:: improper_style umbrella/omp
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improper_style umbrella command
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===============================
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Accelerator Variants: *umbrella/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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improper_style umbrella
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Examples
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""""""""
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.. code-block:: LAMMPS
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improper_style umbrella
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improper_coeff 1 100.0 180.0
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Description
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"""""""""""
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The *umbrella* improper style uses the following potential, which is
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commonly referred to as a classic inversion and used in the
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:doc:`DREIDING <Howto_bioFF>` force field:
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.. math::
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E = & \frac{1}{2}K\left( \frac{1}{\sin\omega_0}\right) ^2 \left( \cos\omega - \cos\omega_0\right) ^2 \qquad \omega_0 \neq 0^o \\
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E = & K\left( 1-cos\omega\right) \qquad \omega_0 = 0^o
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where :math:`K` is the force constant and :math:`\omega` is the angle between the IL
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axis and the IJK plane:
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.. image:: JPG/umbrella.jpg
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:align: center
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If :math:`\omega_0 = 0` the potential term has a minimum for the planar
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structure. Otherwise it has two minima at :math:`\omega +/- \omega_0`,
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with a barrier in between.
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See :ref:`(Mayo) <umbrella-Mayo>` for a description of the DREIDING force field.
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The following coefficients must be defined for each improper type via
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the :doc:`improper_coeff <improper_coeff>` command as in the example
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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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* :math:`K` (energy)
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* :math:`\omega_0` (degrees)
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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 improper style can only be used if LAMMPS was built with the
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MOLECULE package. See the :doc:`Build package <Build_package>` doc page
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for more info.
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Related commands
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""""""""""""""""
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:doc:`improper_coeff <improper_coeff>`
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Default
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"""""""
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none
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----------
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.. _umbrella-Mayo:
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**(Mayo)** Mayo, Olfason, Goddard III, J Phys Chem, 94, 8897-8909
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(1990),
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