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pair_coul_diel.txt
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.. index:: pair_style coul/diel
pair_style coul/diel command
============================
pair_style coul/diel/omp command
================================
Syntax
""""""
.. parsed-literal::
pair_style coul/diel cutoff
cutoff = global cutoff (distance units)
Examples
""""""""
.. parsed-literal::
pair_style coul/diel 3.5
pair_coeff 1 4 78. 1.375 0.112
Description
"""""""""""
Style *coul/diel* computes a Coulomb correction for implict solvent
ion interactions in which the dielectric perimittivity is distance dependent.
The dielectric permittivity epsilon_D(r) connects to limiting regimes:
One limit is defined by a small dielectric permittivity (close to vacuum)
at or close to contact seperation between the ions. At larger separations
the dielectric permittivity reaches a bulk value used in the regular Coulomb
interaction coul/long or coul/cut.
The transition is modeled by a hyperbolic function which is incorporated
in the Coulomb correction term for small ion separations as follows
.. image:: Eqs/pair_coul_diel.jpg
:align: center
where r_me is the inflection point of epsilon_D(r) and sigma_e is a slope
defining length scale. C is the same Coulomb conversion factor as in the
pair_styles coul/cut, coul/long, and coul/debye. In this way the Coulomb
interaction between ions is corrected at small distances r. The lower
limit of epsilon_D(r->0)=5.2 due to dielectric saturation :ref:`(Stiles) <Stiles>`
while the Coulomb interaction reaches its bulk limit by setting
epsilon_D(r->\infty)=epsilon, the bulk value of the solvent which is 78
for water at 298K.
Examples of the use of this type of Coulomb interaction include implicit
solvent simulations of salt ions
:ref:`(Lenart) <Lenart>` and of ionic surfactants :ref:`(Jusufi) <Jusufi>`.
Note that this potential is only reasonable for implicit solvent simulations
and in combiantion with coul/cut or coul/long. It is also usually combined
with gauss/cut, see :ref:`(Lenart) <Lenart>` or :ref:`(Jusufi) <Jusufi>`.
The following coefficients must be defined for each pair of atom
types via the :doc:`pair_coeff <pair_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:
* epsilon (no units)
* r_me (distance units)
* sigma_e (distance units)
The global cutoff (r_c) specified in the pair_style command is used.
----------
**Mixing, shift, table, tail correction, restart, rRESPA info**:
This pair style does not support parameter mixing. Coefficients must be given explicitly for each type of particle pairs.
This pair style supports the :doc:`pair_modify <pair_modify>` shift
option for the energy of the Gauss-potential portion of the pair
interaction.
The :doc:`pair_modify <pair_modify>` table option is not relevant
for this pair style.
This pair style does not support the :doc:`pair_modify <pair_modify>`
tail option for adding long-range tail corrections to energy and
pressure.
This pair style can only be used via the *pair* keyword of the
:doc:`run_style respa <run_style>` command. It does not support the
*inner*, *middle*, *outer* keywords.
Restrictions
""""""""""""
This style is part of the "user-misc" package. It is only enabled
if LAMMPS was built with that package. See the :ref:`Making LAMMPS <2_3>` section for more info.
Related commands
""""""""""""""""
:doc:`pair_coeff <pair_coeff>`
:doc:`pair_style gauss/cut <pair_gauss>`
**Default:** none
----------
.. _Stiles:
**(Stiles)** Stiles , Hubbard, and Kayser, J Chem Phys, 77,
6189 (1982).
.. _Lenart:
**(Lenart)** Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
044509 (2007).
.. _Jusufi:
**(Jusufi)** Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
13783 (2008).
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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