forked from lijiext/lammps
114 lines
3.4 KiB
Plaintext
114 lines
3.4 KiB
Plaintext
.. index:: improper_style ring
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improper_style ring command
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===========================
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improper_style ring/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 ring
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Examples
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""""""""
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.. parsed-literal::
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improper_style ring
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improper_coeff 1 8000 70.5
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Description
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"""""""""""
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The *ring* improper style uses the potential
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.. image:: Eqs/improper_ring.jpg
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:align: center
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where K is a prefactor, theta is the angle formed by the atoms
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specified by (i,j,k,l) indices and theta0 its equilibrium value.
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If the 4 atoms in an improper quadruplet (listed in the data file read
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by the :doc:`read_data <read_data>` command) are ordered i,j,k,l then
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theta_*ijl* is the angle between atoms i,j and l, theta_*ijk* is the
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angle between atoms i,j and k, theta_*kjl* is the angle between atoms
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j,k, and l.
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The "ring" improper style implements the improper potential introduced
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by Destree et al., in Equation (9) of :ref:`(Destree) <Destree>`. This
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potential does not affect small amplitude vibrations but is used in an
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ad-hoc way to prevent the onset of accidentially large amplitude
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fluctuations leading to the occurrence of a planar conformation of the
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three bonds i-j, j-k and j-l, an intermediate conformation toward the
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chiral inversion of a methine carbon. In the "Impropers" section of
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data file four atoms: i, j, k and l are specified with i,j and l lying
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on the backbone of the chain and k specifying the chirality of j.
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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/radian^2)
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* theta0 (degrees)
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theta0 is specified in degrees, but LAMMPS converts it to radians
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internally; hence the units of K are in energy/radian^2.
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----------
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Styles with a *cuda*, *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 USER-CUDA, GPU, USER-INTEL,
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KOKKOS, USER-OMP and OPT packages, respectively. They are only
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enabled if 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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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:`improper_coeff <improper_coeff>`
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.. _Destree:
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**(Destree)** M. Destree, F. Laupretre, A. Lyulin, and J.-P. Ryckaert,
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J Chem Phys, 112, 9632 (2000).
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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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