"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 yukawa/colloid command :h3

[Syntax:]

pair_style yukawa/colloid kappa cutoff :pre

kappa = screening length (inverse distance units)
cutoff = global cutoff for colloidal Yukawa interactions (distance units) :ul

[Examples:]

pair_style yukawa/colloid 2.0 2.5
pair_coeff 1 1 100.0 2.3
pair_coeff * * 100.0 :pre

[Description:]

Style {yukawa/colloid} computes pairwise interactions with the formula

:c,image(Eqs/pair_yukawa_colloid.jpg)

where Ri and Rj are the radii of the two particles and Rc is the
cutoff.

In contrast to "pair_style yukawa"_pair_yukawa.html, this functional
form arises from the Coulombic interaction between two colloid
particles, screened due to the presence of an electrolyte.
"Pair_style yukawa"_pair_yukawa.html is a screened Coulombic potential
between two point-charges and uses no such approximation.

This potential applies to nearby particle pairs for which the Derjagin
approximation holds, meaning h << Ri + Rj, where h is the
surface-to-surface separation of the two particles.

When used in combination with "pair_style colloid"_pair_colloid.html,
the two terms become the so-called DLVO potential, which combines
electrostatic repulsion and van der Waals attraction.

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, or by mixing as described below:

A (energy/distance units)
cutoff (distance units) :ul

The prefactor A is determined from the relationship between surface
charge and surface potential due to the presence of electrolyte.  Note
that the A for this potential style has different units than the A
used in "pair_style yukawa"_pair_yukawa.html.  For low surface
potentials, i.e. less than about 25 mV, A can be written as:

A = 2 * PI * R*eps*eps0 * kappa * psi^2 :pre

where

R = colloid radius (distance units)
eps0 = permittivity of free space (charge^2/energy/distance units)
eps = relative permittivity of fluid medium (dimensionless)
kappa = inverse screening length (1/distance units)
psi = surface potential (energy/charge units) :ul

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

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

For atom type pairs I,J and I != J, the A coefficient and cutoff
distance for this pair style can be mixed.  A is an energy value mixed
like a LJ epsilon.  The default mix value is {geometric}.  See the
"pair_modify" command for details.

This pair style supports the "pair_modify"_pair_modify.html shift
option for the energy of the pair interaction.

The "pair_modify"_pair_modify.html table option is not relevant
for this pair style.

This pair style does not support the "pair_modify"_pair_modify.html
tail option for adding long-range tail corrections to energy and
pressure.

This pair style writes its 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.

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

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[Restrictions:]

This style is part of the "colloid" package.  It is only enabled if
LAMMPS was built with that package.  See the "Making
LAMMPS"_Section_start.html#2_3 section for more info.

This pair style requires that atoms be finite-size spheres with a
diameter, as defined by the "atom_style sphere"_atom_style.html
command.

Per-particle polydispersity is not yet supported by this pair style;
per-type polydispersity is allowed.  This means all particles of the
same type must have the same diameter.  Each type can have a different
diameter.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none
