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

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

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pair_style exp6/rx command :h3

[Syntax:]

pair_style exp6/rx cutoff :pre

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

[Examples:]

pair_style exp6/rx 10.0
pair_coeff * * exp6.params h2o h2o 1.0 1.0 10.0
pair_coeff * * exp6.params h2o 1fluid 1.0 1.0 10.0
pair_coeff * * exp6.params 1fluid 1fluid 1.0 1.0 10.0 :pre

[Description:]

Style {exp6/rx} is used in reaction DPD simulations, where the
coarse-grained (CG) particles are composed of {m} species whose
reaction rate kinetics are determined from a set of {n} reaction rate
equations through the "fix rx"_fix_rx.html command.  The species of
one CG particle can interact with a species in a neighboring CG
particle through a site-site interaction potential model.  The
{exp6/rx} style computes an exponential-6 potential given by

:c,image(Eqs/pair_exp6_rx.jpg)

where the {epsilon} parameter determines the depth of the potential
minimum located at {Rm}, and {alpha} determines the softness of the repulsion.

The coefficients must be defined for each species in a given particle
type via the "pair_coeff"_pair_coeff.html command as in the examples
above, where the first argument is the filename that includes the
exponential-6 parameters for each species.  The file includes the
species tag followed by the {alpha}, {epsilon} and {Rm}
parameters. The format of the file is described below.

The second and third arguments specify the site-site interaction
potential between two species contained within two different
particles.  The species tags must either correspond to the species
defined in the reaction kinetics files specified with the "fix
rx"_fix_rx.html command or they must correspond to the tag "1fluid",
signifying interaction with a product species mixture determined
through a one-fluid approximation.  The interaction potential is
weighted by the geometric average of the concentrations of the two
species.  The coarse-grained potential is stored before and after the
reaction kinetics solver is applied, where the difference is defined
to be the internal chemical energy (uChem).

The fourth and fifth arguments specify the {Rm} and {epsilon} scaling exponents.

The final argument specifies the interaction cutoff.

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The format of a tabulated file is as follows (without the
parenthesized comments):

# exponential-6 parameters for various species      (one or more comment or blank lines) :pre
h2o  exp6  11.00 0.02 3.50                          (species, exp6, alpha, Rm, epsilon)
no2  exp6  13.60 0.01 3.70
...
co2  exp6  13.00 0.03 3.20 :pre

A section begins with a non-blank line whose 1st character is not a
"#"; blank lines or lines starting with "#" can be used as comments
between sections.

Following a blank line, the next N lines list the species and their
corresponding parameters.  The first argument is the species tag, the
second argument is the exp6 tag, the 3rd argument is the {alpha}
parameter (energy units), the 4th argument is the {epsilon} parameter
(energy-distance^6 units), and the 5th argument is the {Rm} parameter
(distance units).  If a species tag of "1fluid" is listed as a pair
coefficient, a one-fluid approximation is specified where a
concentration-dependent combination of the parameters is computed
through the following equations:

:c,image(Eqs/pair_exp6_rx_oneFluid.jpg)

where

:c,image(Eqs/pair_exp6_rx_oneFluid2.jpg)

and xa and xb are the mole fractions of a and b, respectively, which
comprise the gas mixture.

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

This pair style does not support mixing.  Thus, coefficients for all
I,J pairs must be specified explicitly.

This style does not support the "pair_modify"_pair_modify.html shift option
for the energy of the exp() and 1/r^6 portion of the pair interaction.

This style does not support the pair_modify tail option for adding long-range
tail corrections to energy and pressure for the A,C terms in the
pair interaction.

[Restrictions:]

This command is part of the USER-DPD package.  It is only enabled if
LAMMPS was built with that package.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none
