forked from lijiext/lammps
137 lines
3.8 KiB
Plaintext
137 lines
3.8 KiB
Plaintext
.. index:: pair_style coul/diel
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pair_style coul/diel command
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============================
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pair_style coul/diel/omp command
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================================
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Syntax
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""""""
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.. parsed-literal::
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pair_style coul/diel cutoff
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cutoff = global cutoff (distance units)
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Examples
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""""""""
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.. parsed-literal::
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pair_style coul/diel 3.5
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pair_coeff 1 4 78. 1.375 0.112
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Description
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"""""""""""
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Style *coul/diel* 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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.. image:: Eqs/pair_coul_diel.jpg
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:align: center
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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 :ref:`(Stiles) <Stiles>`
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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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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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:ref:`(Lenart) <Lenart>` and of ionic surfactants :ref:`(Jusufi) <Jusufi>`.
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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 :ref:`(Lenart) <Lenart>` or :ref:`(Jusufi) <Jusufi>`.
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The following coefficients must be defined for each pair of atom
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types via the :doc:`pair_coeff <pair_coeff>` 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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:doc:`read_data <read_data>` or :doc:`read_restart <read_restart>`
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commands:
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* epsilon (no units)
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* r_me (distance units)
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* sigma_e (distance units)
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The global cutoff (r_c) specified in the pair_style command is used.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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This pair style does not support parameter mixing. Coefficients must be given explicitly for each type of particle pairs.
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This pair style supports the :doc:`pair_modify <pair_modify>` 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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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 to energy and
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pressure.
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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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Restrictions
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""""""""""""
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This style is part of the "user-misc" package. It is only enabled
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if LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_2_3>` section for more info.
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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:doc:`pair_style gauss/cut <pair_gauss>`
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**Default:** none
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----------
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.. _Stiles:
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**(Stiles)** Stiles , Hubbard, and Kayser, J Chem Phys, 77,
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6189 (1982).
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.. _Lenart:
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**(Lenart)** Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
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044509 (2007).
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.. _Jusufi:
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**(Jusufi)** Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
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13783 (2008).
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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