# pair_style sph/taitwater/morris command

## Syntax

``` LAMMPS
pair_style sph/taitwater/morris
```

## Examples

``` LAMMPS
pair_style sph/taitwater/morris
pair_coeff * * 1000.0 1430.0 1.0 2.4
```

## Description

The sph/taitwater/morris style computes pressure forces between SPH
particles according to Tait\'s equation of state:

$$p = B \biggl[\left(\frac{\rho}{\rho_0}\right)^{\gamma} - 1\biggr]$$

where $\gamma = 7$ and $B = c_0^2 \rho_0 / \gamma$, with $\rho_0$ being
the reference density and $c_0$ the reference speed of sound.

This pair style also computes laminar viscosity [(Morris)](Morris).

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.

-   $\rho_0$ reference density (mass/volume units)
-   $c_0$ reference soundspeed (distance/time units)
-   $\nu$ dynamic viscosity (mass\*distance/time 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

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

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

::: {#Morris}
**(Morris)** Morris, Fox, Zhu, J Comp Physics, 136, 214-226 (1997).
:::