"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

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pair_style coul/diel command :h3
pair_style coul/diel/omp command :h3

[Syntax:]

pair_style coul/diel cutoff :pre

cutoff = global cutoff (distance units)

[Examples:]

pair_style coul/diel 3.5
pair_coeff 1 4 78. 1.375 0.112 :pre


[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

:c,image(Eqs/pair_coul_diel.jpg)

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 "(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 
"(Lenart)"_#Lenart and of ionic surfactants "(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 "(Lenart)"_#Lenart or "(Jusufi)"_#Jusufi.  

The following coefficients must be defined for each pair of atom
types via the "pair_coeff"_pair_coeff.html command as in the example
above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:

epsilon (no units)
r_me (distance units)
sigma_e (distance units) :ul

The global cutoff (r_c) specified in the pair_style command is used.

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[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 "pair_modify"_pair_modify.html shift
option for the energy of the Gauss-potential portion of the pair
interaction.

The "pair_modify"_pair_modify.html table option is not relevant
for this pair style.

This pair style does not support the "pair_modify"_pair_modify.html
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
"run_style respa"_run_style.html 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 "Making
LAMMPS"_Section_start.html#2_3 section for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html
"pair_style gauss/cut"_pair_gauss.html

[Default:] none

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:link(Stiles)
[(Stiles)] Stiles , Hubbard, and Kayser, J Chem Phys, 77,
6189 (1982).

:link(Lenart)
[(Lenart)] Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
044509 (2007).

:link(Jusufi)
[(Jusufi)] Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
13783 (2008).