pair_style coul/tt command

Syntax

pair_style style args
  • style = coul/tt

  • args = list of arguments for a particular style

coul/tt args = n cutoff
  n = degree of polynomial
  cutoff = global cutoff (distance units)

Examples

pair_style hybrid/overlay ... coul/tt 4 12.0
pair_coeff 1 2  coul/tt 4.5 1.0
pair_coeff 1 2  coul/tt 4.0 1.0 4 12.0
pair_coeff 1 3* coul/tt 4.5 1.0 4

Description

The coul/tt pair style is meant to be used with force fields that include explicit polarization through Drude dipoles.

The coul/tt pair style should be used as a sub-style within in the pair_style hybrid/overlay command, in conjunction with a main pair style including Coulomb interactions and thole pair style, or with lj/cut/thole/long pair style that is equivalent to the combination of preceding two.

The coul/tt pair styles compute the charge-dipole Coulomb interaction damped at short distances by a function

\[f_{n,ij}(r) = 1 - c_{ij} \cdot e^{-b_{ij} r} \sum_{k=0}^n \frac{(b_{ij} r)^k}{k!}\]

This function results from an adaptation to the Coulomb interaction (Salanne) of the damping function originally proposed by Tang Toennies for van der Waals interactions.

The polynomial takes the degree 4 for damping the Coulomb interaction. The parameters \(b_{ij}\) and \(c_{ij}\) could be determined from first-principle calculations for small, mainly mono-atomic, ions (Salanne), or else treated as empirical for large molecules.

In pair styles with Drude induced dipoles, this damping function is typically applied to the interactions between a Drude charge (either \(q_{D,i}\) on a Drude particle or \(-q_{D,i}\) on the respective Drude core)) and a charge on a non-polarizable atom, \(q_{j}\).

The Tang-Toennies function could also be used to damp electrostatic interactions between the (non-polarizable part of the) charge of a core, \(q_{i}-q_{D,i}\), and the Drude charge of another, \(-q_{D,j}\). The \(b_{ij}\) and \(c_{ij}\) are equal to \(b_{ji}\) and \(c_{ji}\) in the case of core-core interactions.

For pair_style coul/tt, the following coefficients must be defined for each pair of atoms types via the pair_coeff command as in the example above.

  • \(b_{ij}\)

  • \(c_{ij}\)

  • degree of polynomial (positive integer)

  • cutoff (distance units)

The last two coefficients are optional. If not specified the global degree of the polynomial or the global cutoff specified in the pair_style command are used. In order to specify a cutoff (forth argument), the degree of the polynomial (third argument) must also be specified.


Mixing, shift, table, tail correction, restart, rRESPA info

The coul/tt pair style does not support mixing. Thus, coefficients for all I,J pairs must be specified explicitly.

Restrictions

These pair styles are part of the USER-DRUDE package. They are only enabled if LAMMPS was built with that package. See the Build package doc page for more info.

This pair_style should currently not be used with the charmm dihedral style if the latter has non-zero 1-4 weighting factors. This is because the coul/tt pair style does not know which pairs are 1-4 partners of which dihedrals.

Default

none


(Thole) Chem Phys, 59, 341 (1981).

(Salanne) Salanne, Rotenberg, Jahn, Vuilleumier, Simon, Christian and Madden, Theor Chem Acc, 131, 1143 (2012).

(Tang and Toennies) J Chem Phys, 80, 3726 (1984).