2011-12-01 23:36:19 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<H3>pair_style coul/diel command
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</H3>
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2014-05-03 05:47:08 +08:00
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<H3>pair_style coul/diel/omp command
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</H3>
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2011-12-01 23:36:19 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style coul/diel cutoff
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</PRE>
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<P>cutoff = global cutoff (distance units)
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</P>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style coul/diel 3.5
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pair_coeff 1 4 78. 1.375 0.112
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>coul/diel</I> computes a Coulomb correction for implict solvent
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ion interactions in which the dielectric perimittivity is distance dependent.
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The dielectric permittivity epsilon_D(r) connects to limiting regimes:
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One limit is defined by a small dielectric permittivity (close to vacuum)
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at or close to contact seperation between the ions. At larger separations
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the dielectric permittivity reaches a bulk value used in the regular Coulomb
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interaction coul/long or coul/cut.
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The transition is modeled by a hyperbolic function which is incorporated
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in the Coulomb correction term for small ion separations as follows
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</P>
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<CENTER><IMG SRC = "Eqs/pair_coul_diel.jpg">
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</CENTER>
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<P>where r_me is the inflection point of epsilon_D(r) and sigma_e is a slope
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defining length scale. C is the same Coulomb conversion factor as in the
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pair_styles coul/cut, coul/long, and coul/debye. In this way the Coulomb
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interaction between ions is corrected at small distances r. The lower
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limit of epsilon_D(r->0)=5.2 due to dielectric saturation <A HREF = "#Stiles">(Stiles)</A>
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while the Coulomb interaction reaches its bulk limit by setting
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epsilon_D(r->\infty)=epsilon, the bulk value of the solvent which is 78
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for water at 298K.
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</P>
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<P>Examples of the use of this type of Coulomb interaction include implicit
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solvent simulations of salt ions
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<A HREF = "#Lenart">(Lenart)</A> and of ionic surfactants <A HREF = "#Jusufi">(Jusufi)</A>.
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Note that this potential is only reasonable for implicit solvent simulations
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and in combiantion with coul/cut or coul/long. It is also usually combined
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with gauss/cut, see <A HREF = "#Lenart">(Lenart)</A> or <A HREF = "#Jusufi">(Jusufi)</A>.
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</P>
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<P>The following coefficients must be defined for each pair of atom
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types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the example
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above, or in the data file or restart files read by the
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<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
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commands:
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</P>
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<UL><LI>epsilon (no units)
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<LI>r_me (distance units)
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<LI>sigma_e (distance units)
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</UL>
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<P>The global cutoff (r_c) specified in the pair_style command is used.
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</P>
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<HR>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>This pair style does not support parameter mixing. Coefficients must be given explicitly for each type of particle pairs.
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</P>
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<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
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option for the energy of the Gauss-potential portion of the pair
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interaction.
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</P>
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<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
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for this pair style.
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</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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tail option for adding long-range tail corrections to energy and
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pressure.
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</P>
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<P>This pair style can only be used via the <I>pair</I> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. It does not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<P><B>Restrictions:</B>
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</P>
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2011-12-09 07:17:25 +08:00
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<P>This style is part of the "user-misc" package. It is only enabled
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2011-12-01 23:36:19 +08:00
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if LAMMPS was built with that package. See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "pair_coeff.html">pair_coeff</A>
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<A HREF = "pair_gauss.html">pair_style gauss/cut</A>
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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<A NAME = "Stiles"></A>
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<P><B>(Stiles)</B> Stiles , Hubbard, and Kayser, J Chem Phys, 77,
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6189 (1982).
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</P>
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<A NAME = "Lenart"></A>
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<P><B>(Lenart)</B> Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
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044509 (2007).
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</P>
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<A NAME = "Jusufi"></A>
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<P><B>(Jusufi)</B> Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
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13783 (2008).
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</P>
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</HTML>
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