forked from lijiext/lammps
111 lines
2.8 KiB
Plaintext
111 lines
2.8 KiB
Plaintext
.. index:: improper_style umbrella
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improper_style umbrella command
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===============================
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improper_style umbrella/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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improper_style umbrella
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Examples
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""""""""
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.. parsed-literal::
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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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:ref:`DREIDING <howto_4>` force field:
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.. image:: Eqs/improper_umbrella.jpg
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:align: center
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where K is the force constant and omega is the angle between the IL
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axis and the IJK plane:
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.. image:: Eqs/umbrella.jpg
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:align: center
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If omega0 = 0 the potential term has a minimum for the planar
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structure. Otherwise it has two minima at +/- omega0, with a barrier
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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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* K (energy)
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* omega0 (degrees)
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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 improper style can only be used if LAMMPS was built with the
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MOLECULE package (which it is by default). See the :ref:`Making LAMMPS <start_3>` section for more info on packages.
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Related commands
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""""""""""""""""
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:doc:`improper_coeff <improper_coeff>`
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**Default:** 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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.. _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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