# pair_style brownian command

Accelerator Variants: *brownian/omp*

# pair_style brownian/poly command

Accelerator Variants: *brownian/poly/omp*

## Syntax

``` LAMMPS
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

``` LAMMPS
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](pair_lubricate) or [pair_style lubricateU](pair_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](pair_coeff) command as in the examples above, or in
the data file or restart files read by the [read_data](read_data) or
[read_restart](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](Speed_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](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](Run_options) when you invoke LAMMPS, or you can use the
[suffix](suffix) command in your input script.

See the [Accelerator packages](Speed_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 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](pair_modify) shift
option for the energy of the pair interaction.

The [pair_modify](pair_modify) table option is not relevant for this
pair style.

This pair style does not support the [pair_modify](pair_modify) tail
option for adding long-range tail corrections to energy and pressure.

This pair style writes its information to [binary restart
files](restart), 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) command. It does 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](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.

## Related commands

[pair_coeff](pair_coeff), [pair_style lubricate](pair_lubricate),
[pair_style lubricateU](pair_lubricateU)

## Default

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