Syntax:
pair_style yukawa/colloid kappa cutoff
Examples:
pair_style yukawa/colloid 2.0 2.5 pair_coeff 1 1 100.0 2.3 pair_coeff * * 100.0
Description:
Style yukawa/colloid computes pairwise interactions with the formula
where Ri and Rj are the radii of the two particles and Rc is the cutoff.
In contrast to pair_style yukawa, this functional form arises from the Coulombic interaction between two colloid particles, screened due to the presence of an electrolyte. Pair_style yukawa 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, 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 command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands, or by mixing as described below:
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. 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
where
The last coefficient is optional. If not specified, the global yukawa/colloid cutoff is used.
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 shift option for the energy of the pair interaction.
The pair_modify table option is not relevant for this pair style.
This pair style does not support the pair_modify tail option for adding long-range tail corrections to energy and pressure.
This pair style writes its information to binary restart files, 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 command. It does not support the inner, middle, outer keywords.
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 for more info.
Because this potential uses the radii of the particles, the atom style must support particles whose size is set via the shape command. For example atom_style colloid or ellipsoid. Only spherical particles are currently allowed for pair_style yukawa/colloid, which means that for each particle type, its 3 shape diameters must be equal to each other.
Related commands:
Default: none