# pair_style coul/slater/long command

## Syntax

pair_style coul/slater/cut lambda cutoff
pair_style coul/slater/long lambda cutoff


lambda = decay length of the charge (distance units) cutoff = cutoff (distance units)

## Examples

pair_style coul/slater/cut 1.0 3.5
pair_coeff * *
pair_coeff 2 2 2.5

pair_style coul/slater/long 1.0 12.0
pair_coeff * *
pair_coeff 1 1 5.0


## Description

Styles coul/slater compute electrostatic interactions in mesoscopic models which employ potentials without explicit excluded-volume interactions. The goal is to prevent artificial ionic pair formation by including a charge distribution in the Coulomb potential, following the formulation of (Melchor):

$E = \frac{Cq_iq_j}{\epsilon r} \left( 1- \left( 1 + \frac{r_{ij}}{\lambda} exp\left( -2r_{ij}/\lambda \right) \right) \right) \qquad r < r_c$

where $$r_c$$ is the cutoff distance and $$\lambda$$ is the decay length of the charge. C is the same Coulomb conversion factor as in the pair_styles coul/cut and coul/long. In this way the Coulomb interaction between ions is corrected at small distances r. For the coul/slater/cut style, the potential energy for distances larger than the cutoff is zero, while for the coul/slater/long, the long-range interactions are computed either by the Ewald or the PPPM technique.

Phenomena that can be captured at a mesoscopic level using this type of electrostatic interactions include the formation of polyelectrolyte-surfactant aggregates, charge stabilization of colloidal suspensions, and the formation of complexes driven by charged species in biological systems. (Vaiwala).

The cutoff distance is optional. If it is not used, the default global value specified in the pair_style command is used. For each pair of atom types, a specific cutoff distance can be defined via the pair_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:

• $$r_c$$ (distance units)

The global decay length of the charge ($$\lambda$$) specified in the pair_style command is used for all pairs.

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

For atom type pairs I,J and I != J, the cutoff distance for the coul/slater styles can be mixed. The default mix value is geometric. See the “pair_modify” command for details.

The pair_modify shift and table options are not relevant for these pair styles.

These pair styles do not support the pair_modify tail option for adding long-range tail corrections to energy and pressure.

These pair styles write their information to binary restart files, so pair_style and pair_coeff commands do not need to be specified in an input script that reads a restart file.

This pair style can only be used via the pair keyword of the run_style respa command. It does not support the inner, middle, outer keywords.

## Restrictions

The coul/slater/long style requires the long-range solvers included in the KSPACE package.

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