103 lines
3.4 KiB
ReStructuredText
103 lines
3.4 KiB
ReStructuredText
.. index:: improper_style ring
|
|
|
|
improper_style ring command
|
|
===========================
|
|
|
|
improper_style ring/omp command
|
|
===============================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
improper_style ring
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
.. code-block:: LAMMPS
|
|
|
|
improper_style ring
|
|
improper_coeff 1 8000 70.5
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
The *ring* improper style uses the potential
|
|
|
|
.. math::
|
|
|
|
E = &\frac{1}{6} K \left(\Delta_{ijl} + \Delta_{ijk} + \Delta_{kjl} \right)^6 \\
|
|
\Delta_{ijl} = & \cos{\theta_{ijl} - \cos{\theta_0}} \\
|
|
\Delta_{ijk} = & \cos{\theta_{ijk} - \cos{\theta_0}} \\
|
|
\Delta_{kjl} = & \cos{\theta_{kjl} - \cos{\theta_0}}
|
|
|
|
where :math:`K` is a prefactor, :math:`\theta` is the angle formed by
|
|
the atoms specified by (i,j,k,l) indices and :math:`\theta_0` its
|
|
equilibrium value.
|
|
|
|
If the 4 atoms in an improper quadruplet (listed in the data file read
|
|
by the :doc:`read_data <read_data>` command) are ordered i,j,k,l then
|
|
:math:`\theta_{ijl}` is the angle between atoms i,j and l,
|
|
:math:`\theta_{ijk}` is the angle between atoms i,j and k,
|
|
:math:`\theta_{kjl}` is the angle between atoms j,k, and l.
|
|
|
|
The "ring" improper style implements the improper potential introduced
|
|
by Destree et al., in Equation (9) of :ref:`(Destree) <Destree>`. This
|
|
potential does not affect small amplitude vibrations but is used in an
|
|
ad-hoc way to prevent the onset of accidentally large amplitude
|
|
fluctuations leading to the occurrence of a planar conformation of the
|
|
three bonds i-j, j-k and j-l, an intermediate conformation toward the
|
|
chiral inversion of a methine carbon. In the "Impropers" section of
|
|
data file four atoms: i, j, k and l are specified with i,j and l lying
|
|
on the backbone of the chain and k specifying the chirality of j.
|
|
|
|
The following coefficients must be defined for each improper type via
|
|
the :doc:`improper_coeff <improper_coeff>` command as in the example
|
|
above, or in the data file or restart files read by the
|
|
:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
|
|
commands:
|
|
|
|
* :math:`K` (energy)
|
|
* :math:`\theta_0` (degrees)
|
|
|
|
----------
|
|
|
|
Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
|
|
functionally the same as the corresponding style without the suffix.
|
|
They have been optimized to run faster, depending on your available
|
|
hardware, as discussed on the :doc:`Speed packages <Speed_packages>` doc
|
|
page. The accelerated styles take the same arguments and should
|
|
produce the same results, except for round-off and precision issues.
|
|
|
|
These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
|
|
USER-OMP and OPT packages, respectively. They are only enabled if
|
|
LAMMPS was built with those packages. See the :doc:`Build package <Build_package>` doc page for more info.
|
|
|
|
You can specify the accelerated styles explicitly in your input script
|
|
by including their suffix, or you can use the :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
|
|
:doc:`suffix <suffix>` command in your input script.
|
|
|
|
See the :doc:`Speed packages <Speed_packages>` doc page for more
|
|
instructions on how to use the accelerated styles effectively.
|
|
|
|
----------
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
|
|
This improper style can only be used if LAMMPS was built with the
|
|
USER-MISC package. See the :doc:`Build package <Build_package>` doc
|
|
page for more info.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`improper_coeff <improper_coeff>`
|
|
|
|
.. _Destree:
|
|
|
|
**(Destree)** M. Destree, F. Laupretre, A. Lyulin, and J.-P. Ryckaert,
|
|
J Chem Phys, 112, 9632 (2000).
|