"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)

:line

pair_style mm3/switch3/coulgauss/long command :h3

[Syntax:]

pair_style style args :pre

style = {mm3/switch3/coulgauss/long}
args = list of arguments for a particular style :ul
  {mm3/switch3/coulgauss/long} args = cutoff (cutoff2) width
    cutoff  = global cutoff for MM3 (and Coulombic if only 1 arg) (distance units)
    cutoff2 = global cutoff for Coulombic (optional) (distance units)
    width  = width parameter of the smoothing function (distance units) :pre

[Examples:]

pair_style mm3/switch3/coulgauss/long    12.0 3.0
pair_coeff 1  0.2 2.5 1.2 :pre

pair_style mm3/switch3/coulgauss/long   12.0 10.0 3.0
pair_coeff 1  0.2 2.5 1.2 :pre

[Description:]

The {mm3/switch3/coulgauss} style evaluates the MM3
vdW potential "(Allinger)"_#mm3-allinger1989

:c,image(Eqs/pair_mm3_switch3.jpg)

, which goes smoothly to zero at the cutoff r_c as defined
by the switching function

:c,image(Eqs/pair_switch3.jpg)

where w is the width defined in the arguments. This potential
is combined with Coulomb interaction between Gaussian charge densities:

:c,image(Eqs/pair_coulgauss.jpg)

where qi and qj are the
charges on the 2 atoms, epsilon is the dielectric constant which
can be set by the "dielectric"_dielectric.html command, gamma_i and gamma_j
are the widths of the Gaussian charge distribution and erf() is the error-function.
This style has to be used in conjunction with the "kspace_style"_kspace_style.html command

If one cutoff is specified it is used for both the vdW and Coulomb
terms.  If two cutoffs are specified, the first is used as the cutoff
for the vdW terms, and the second is the cutoff for the Coulombic term.

The following coefficients must be defined for each pair of atoms
types via the "pair_coeff"_pair_coeff.html command as in the examples
above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:

epsilon (energy)
r_v (distance)
gamma (distance) :ul

:line

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

Mixing rules are fixed for this style as defined above.

Shifting the potential energy is not necessary because the switching
function ensures that the potential is zero at the cut-off.


[Restrictions:]

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

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none

