"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)

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pair_style gauss command :h3
pair_style gauss/gpu command :h3
pair_style gauss/omp command :h3
pair_style gauss/cut command :h3
pair_style gauss/cut/omp command :h3

[Syntax:]

pair_style gauss cutoff
pair_style gauss/cut cutoff :pre

cutoff = global cutoff for Gauss interactions (distance units) :ul

[Examples:]

pair_style gauss 12.0
pair_coeff * * 1.0 0.9
pair_coeff 1 4 1.0 0.9 10.0 :pre

pair_style gauss/cut 3.5
pair_coeff 1 4 0.2805 1.45 0.112 :pre


[Description:]

Style {gauss} computes a tethering potential of the form

:c,image(Eqs/pair_gauss.jpg)

between an atom and its corresponding tether site which will typically
be a frozen atom in the simulation.  Rc is the cutoff.

The following coefficients must be defined for each pair of atom 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:

A (energy units)
B (1/distance^2 units)
cutoff (distance units) :ul

The last coefficient is optional. If not specified, the global cutoff
is used.

Style {gauss/cut} computes a generalized Gaussian interaction potential
between pairs of particles:

:c,image(Eqs/pair_gauss_cut.jpg)

where H determines together with the standard deviation sigma_h the
peak height of the Gaussian function, and r_mh the peak position.
Examples of the use of the Gaussian potentials include implicit
solvent simulations of salt ions "(Lenart)"_#Lenart2 and of surfactants
"(Jusufi)"_#Jusufi2.  In these instances the Gaussian potential mimics
the hydration barrier between a pair of particles. The hydration
barrier is located at r_mh and has a width of sigma_h. The prefactor
determines the height of the potential barrier.

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

H (energy * distance units)
r_mh (distance units)
sigma_h (distance units)
cutoff (distance units) :ul

The last coefficient is optional. If not specified, the global cutoff
is used.

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Styles with a {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed on the "Speed packages"_Speed_packages.html doc
page.  The accelerated styles take the same arguments and should
produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively.  They are only enabled if
LAMMPS was built with those packages.  See the "Build
package"_Build_package.html doc page for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the "-suffix command-line
switch"_Run_options.html when you invoke LAMMPS, or you can use the
"suffix"_suffix.html command in your input script.

See the "Speed packages"_Speed_packages.html doc page for more
instructions on how to use the accelerated styles effectively.

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

For atom type pairs I,J and I != J, the A, B, H, sigma_h, r_mh
parameters, and the cutoff distance for these pair styles can be mixed:
A (energy units)
sqrt(1/B) (distance units, see below)
H (energy units)
sigma_h (distance units)
r_mh (distance units)
cutoff (distance units):ul

The default mix value is {geometric}.
Only {arithmetic} and {geometric} mix values are supported.
See the "pair_modify" command for details.

The A and H parameters are mixed using the same rules normally
used to mix the "epsilon" parameter in a Lennard Jones interaction.
The sigma_h, r_mh, and the cutoff distance are mixed using the same
rules used to mix the "sigma" parameter in a Lennard Jones interaction.
The B parameter is converted to a distance (sigma), before mixing
(using sigma=B^-0.5), and converted back to a coefficient
afterwards (using B=sigma^2).
Negative A values are converted to positive A values (using abs(A))
before mixing, and converted back after mixing
(by multiplying by min(sign(Ai),sign(Aj))).
This way, if either particle is repulsive (if Ai<0 or Aj<0),
then the default interaction between both particles will be repulsive.

The {gauss} style does not support the "pair_modify"_pair_modify.html
shift option. There is no effect due to the Gaussian well beyond the
cutoff; hence reasonable cutoffs need to be specified.

The {gauss/cut} style supports the "pair_modify"_pair_modify.html shift
option for the energy of the Gauss-potential portion of the pair
interaction.

The "pair_modify"_pair_modify.html table and tail options are not
relevant for these pair styles.

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

These pair styles can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  They do not support the
{inner}, {middle}, {outer} keywords.

The {gauss} pair style tallies an "occupancy" count of how many Gaussian-well
sites have an atom within the distance at which the force is a maximum
= sqrt(0.5/b).  This quantity can be accessed via the "compute
pair"_compute_pair.html command as a vector of values of length 1.

To print this quantity to the log file (with a descriptive column
heading) the following commands could be included in an input script:

compute gauss all pair gauss
variable occ equal c_gauss\[1\]
thermo_style custom step temp epair v_occ :pre

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[Restrictions:]

The {gauss/cut} style is part of the "user-misc" package. It is only
enabled if LAMMPS is build with that package.  See the "Build
package"_Build_package.html doc page for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html,
"pair_style coul/diel"_pair_coul_diel.html

[Default:] none

:link(Lenart2)
[(Lenart)] Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
044509 (2007).

:link(Jusufi2)
[(Jusufi)] Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
13783 (2008).

