shifted force Lennard-Jones with Coulomb interactions pair style

Dear all:

I combined the Coulomb calculations with shifted force Lennard-Jones interactions into a new pair_style called lj/sf/coul/long.

It it based on the lj/sf and lj/cut/coul/long pair_styles.

Enclosed are the source files, if you want to add them to the USER-MISC directory of the source code.

The USER-MISC/README additional line should read
"
pair_style lj/sf/coul/long, Jacob Wagner (U Chicago), jwwagner at uchicago.edu, 12 Aug 14

"

There are only two additions that should be needed for the documentation of the lj/sf page to also accommodate lj/sf/coul/long. The additions are mostly lifted from the pair_lj doc pages.

The header of the doc page would be updated to

"

pair_style lj/sf command### pair_style lj/sf/omp command### pair_style lj/sf/coul/long command

Syntax:

pair_style lj/sf cutoff 


- cutoff = global cutoff for Lennard-Jones interactions (distance units) 

pair_style lj/sf/coul/long cutoff (cutoff2)
  • cutoff = global cutoff for Lennard-Jones interactions (and Coulombic if only 1 arg) (distance units)
  • cutoff2 = global cutoff for Coulombic interactions (optional) (distance units)
**Examples:**

pair_style lj/sf 2.5
pair_coeff * * 1.0 1.0 

pair_coeff 1 1 1.0 1.0 3.0

pair_style lj/sf/coul/long 2.5 2.5
pair_style lj/sf/coul/long 2.5

pair_coef * * 1.0 1.0
pair_coef 1 1 1.0 1.0 3.0
"

The body of the documentation should be expanded to include the following:
"

Style lj/sf/coul/long adds a Coulombic pairwise interaction given by

where C is an energy-conversion constant, Qi and Qj are the charges on the 2 atoms, and epsilon is the dielectric constant which can be set by the dielectric command. If one cutoff is specified in the pair_style command, it is used for both the LJ and Coulombic terms. If two cutoffs are specified, they are used as cutoffs for the LJ and Coulombic terms respectively.

An additional damping factor is applied to the Coulombic term so it can be used in conjunction with the kspace command and its ewald or pppm option. The Coulombic cutoff specified for this style means that pairwise interactions within this distance are computed directly; interactions outside that distance are computed in reciprocal space.

"

From,

Jacob Wagner

University of Chicago

coulomb.png

pair_lj_sf_coul_long.cpp (31.2 KB)

pair_lj_sf_coul_long.h (2.49 KB)