.. 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) ` 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) ` and of ionic surfactants :ref:`(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) ` or :ref:`(Jusufi) `. The following coefficients must be defined for each pair of atom types via the :doc:`pair_coeff ` command as in the example above, or in the data file or restart files read by the :doc:`read_data ` or :doc:`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 ` shift option for the energy of the Gauss-potential portion of the pair interaction. The :doc:`pair_modify ` table option is not relevant for this pair style. This pair style does not support the :doc:`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 ` 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 ` :doc:`pair_style gauss/cut ` **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