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pair_style lubricate command

Syntax:

pair_style lubricate mu squeeze shear pump twist cutinner cutoff 

Examples:

pair_style lubricate 1.5 1 1 1 0 2.3 2.4
pair_coeff 1 1 1.8 2.0
pair_coeff * * 

Description:

Style lubricate computes pairwise interactions between mono-disperse spherical particles with the formula in Appendix A of (Ball and Melrose) which has 4 terms describing different types of lubrication forces between pairs of particles in a background implicit solvent, each of which is proportional in strength to the viscosity of the solvent mu.

These pair-wise forces and torques are a combination of four modes of pair-wise interaction: squeezing, shearing, pumping, and twisting. Each of these modes can be turned on or off with flags in the pair_style command.

Unlike most pair potentials, the two specified cutoffs (cutinner and cutoff) refer to the surface-to-surface separation between two particles, not center-to-center distance. Currently, this pair style can only be used for mono-disperse spheres (same radii), so that separation is r_ij - 2*radius, where r_ij is the center-to-center distance between the particles. Within the inner cutoff cutinner, the forces and torques are evaluated at a separation of cutinner. The outer cutoff is the separation distance beyond which the pair-wise forces are zero.

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 two coefficients are optional. If neither is specified, the two cutoffs specified in the pair_style command are used. Otherwise both must be specified.


Mixing, shift, table, tail correction, per-atom energy/stress, restart, rRESPA info:

For atom type pairs I,J and I != J, the two cutoff distances for this pair style can be mixed. The default mix value is geometric. See the "pair_modify" command for details.

This pair style does not support 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 does not calculate per-atom energy and stress, as used by the compute epair/atom, compute stress/atom, and dump custom commands.

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:

Because this poential computes forces and torques on particles, the atom style must support particles whose size is set via the shape command. This is atom_style ellipsoid and dipole. Since only spherical mono-disperse particles are currently allowed for pair_style lubricate, this means the 3 shape radii for all particle types must be the same.

Related commands:

pair_coeff

Default: none


(Ball) Ball and Melrose, Physica A, 247, 444-472 (1997).