# pair_style sph/lj command

## Syntax

``` LAMMPS
pair_style sph/lj
```

## Examples

``` LAMMPS
pair_style sph/lj
pair_coeff * * 1.0 2.4
```

## Description

The sph/lj style computes pressure forces between particles according to
the Lennard-Jones equation of state, which is computed according to
Ree\'s 1980 polynomial fit [(Ree)](Ree). The Lennard-Jones parameters
epsilon and sigma are set to unity. This pair style also computes
Monaghan\'s artificial viscosity to prevent particles from
interpenetrating [(Monaghan)](Monoghan).

See [this PDF guide](PDF/SPH_LAMMPS_userguide.pdf)\_ to using SPH in
LAMMPS.

The following coefficients must be defined for each pair of atoms types
via the [pair_coeff](pair_coeff) command as in the examples above.

-   $\nu$ artificial viscosity (no units)
-   h kernel function cutoff (distance units)

------------------------------------------------------------------------

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

This style does not support mixing. Thus, coefficients for all I,J pairs
must be specified explicitly.

This style does not support the [pair_modify](pair_modify) shift, table,
and tail options.

This style does not write information to [binary restart
files](restart). Thus, you need to re-specify the pair_style and
pair_coeff commands in an input script that reads a restart file.

This 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

As noted above, the Lennard-Jones parameters epsilon and sigma are set
to unity.

This pair style is part of the SPH package. It is only enabled if LAMMPS
was built with that package. See the [Build package](Build_package) page
for more info.

## Related commands

[pair_coeff](pair_coeff), pair_sph/rhosum

## Default

none

------------------------------------------------------------------------

::: {#Ree}
**(Ree)** Ree, Journal of Chemical Physics, 73, 5401 (1980).
:::

::: {#Monoghan}
**(Monaghan)** Monaghan and Gingold, Journal of Computational Physics,
52, 374-389 (1983).
:::