\(\renewcommand{\AA}{\text{Å}}\)

# pair_style brownian command

Accelerator Variants: brownian/omp, brownian/kk

# pair_style brownian/poly command

Accelerator Variants: brownian/poly/omp

## Syntax

    pair_style style mu flaglog flagfld cutinner cutoff t_target seed flagHI flagVF

- style = brownian or brownian/poly

- mu = dynamic viscosity (dynamic viscosity units)

- flaglog = 0/1 log terms in the lubrication approximation on/off

- flagfld = 0/1 to include/exclude Fast Lubrication Dynamics effects

- cutinner = inner cutoff distance (distance units)

- cutoff = outer cutoff for interactions (distance units)

- t_target = target temp of the system (temperature units)

- seed = seed for the random number generator (positive integer)

- flagHI (optional) = 0/1 to include/exclude 1/r hydrodynamic interactions

- flagVF (optional) = 0/1 to include/exclude volume fraction corrections in the long-range isotropic terms

## Examples

    pair_style brownian 1.5 1 1 2.01 2.5 2.0 5878567 # (assuming radius = 1)
    pair_coeff 1 1 2.05 2.8
    pair_coeff * *

## Description

Styles brownian and brownian/poly compute Brownian forces and torques on finite-size spherical particles. The former requires monodisperse spherical particles; the latter allows for polydisperse spherical particles.

These pair styles are designed to be used with either the pair_style lubricate or pair_style lubricateU commands to provide thermostatting when dissipative lubrication forces are acting. Thus the parameters mu, flaglog, flagfld, cutinner, and cutoff should be specified consistent with the settings in the lubrication pair styles. For details, refer to either of the lubrication pair styles.

The t_target setting is used to specify the target temperature of the system. The random number seed is used to generate random numbers for the thermostatting procedure.

The flagHI and flagVF settings are optional. Neither should be used, or both must be defined.

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:

- cutinner (distance units)

- cutoff (distance units)

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.

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 Accelerator packages 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, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package 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 when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

## Mixing, shift, table, tail correction, restart, rRESPA info

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

These pair styles do not support the pair_modify shift option for the energy of the pair interaction.

The pair_modify table option is not relevant for these pair styles.

These pair styles do not support the pair_modify tail option for adding long-range tail corrections to energy and pressure.

These pair styles write their 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.

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

## Restrictions

These styles are part of the COLLOID package. They are only enabled if LAMMPS was built with that package. See the Build package page for more info.

Only spherical monodisperse particles are allowed for pair_style brownian.

Only spherical particles are allowed for pair_style brownian/poly.

These pair styles are only compatible with the following wall fixes: doc:fix wall/lj93, fix wall/lj126, fix wall/lj1043, fix wall/colloid, fix wall/harmonic, fix wall/lepton, fix wall/morse, fix wall/table <fix_wall>.

## Related commands

pair_coeff, pair_style lubricate, pair_style lubricateU

## Default

The default settings for the optional args are flagHI = 1 and flagVF = 1.