forked from lijiext/lammps
118 lines
3.5 KiB
ReStructuredText
118 lines
3.5 KiB
ReStructuredText
.. index:: pair_style beck
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pair_style beck command
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=======================
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pair_style beck/gpu command
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===========================
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pair_style beck/omp command
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===========================
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Syntax
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""""""
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.. code-block:: LAMMPS
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pair_style beck Rc
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* Rc = cutoff for interactions (distance units)
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Examples
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""""""""
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.. code-block:: LAMMPS
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pair_style beck 8.0
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pair_coeff * * 399.671876712 0.0000867636112694 0.675 4.390 0.0003746
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pair_coeff 1 1 399.671876712 0.0000867636112694 0.675 4.390 0.0003746 6.0
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Description
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"""""""""""
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Style *beck* computes interactions based on the potential by
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:ref:`(Beck) <Beck>`, originally designed for simulation of Helium. It
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includes truncation at a cutoff distance Rc.
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.. math::
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E(r) &= A \exp\left[-\alpha r - \beta r^6\right] - \frac{B}{\left(r^2+a^2\right)^3} \left(1+\frac{2.709+3a^2}{r^2+a^2}\right) \qquad r < R_c \\
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The following coefficients must be defined for each pair of atoms
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types via the :doc:`pair_coeff <pair_coeff>` command as in the examples
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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:`A` (energy units)
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* :math:`B` (energy-distance\^6 units)
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* :math:`a` (distance units)
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* :math:`\alpha` (1/distance units)
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* :math:`\beta` (1/distance\^6 units)
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* cutoff (distance units)
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The last coefficient is optional. If not specified, the global cutoff
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:math:`R_c` is used.
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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 on the :doc:`Speed packages <Speed_packages>` doc
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page. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision 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 :doc:`Build package <Build_package>` doc page 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 :doc:`-suffix command-line switch <Run_options>` when you invoke LAMMPS, or you can use the
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:doc:`suffix <suffix>` command in your input script.
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See the :doc:`Speed packages <Speed_packages>` doc page for more
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instructions on how to use the accelerated styles effectively.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, coefficients must be specified.
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No default mixing rules are used.
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This pair style does not support the :doc:`pair_modify <pair_modify>` shift
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option for the energy of the pair interaction.
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The :doc:`pair_modify <pair_modify>` table option is not relevant
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for this pair style.
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This pair style does not support the :doc:`pair_modify <pair_modify>`
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tail option for adding long-range tail corrections.
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This pair style writes its information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands do not need
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to be specified in an input script that reads a restart file.
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This pair style can only be used via the *pair* keyword of the
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:doc:`run_style respa <run_style>` command. It does not support the
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*inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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none
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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**Default:** none
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----------
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.. _Beck:
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**(Beck)** Beck, Molecular Physics, 14, 311 (1968).
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