# pair_style smd/hertz command

## Syntax

pair_style smd/hertz scale_factor


## Examples

pair_style smd/hertz 1.0
pair_coeff 1 1 <contact_stiffness>


## Description

The smd/hertz style calculates contact forces between SPH particles belonging to different physical bodies.

The contact forces are calculated using a Hertz potential, which evaluates the overlap between two particles (whose spatial extents are defined via its contact radius). The effect is that a particles cannot penetrate into each other. The parameter <contact_stiffness> has units of pressure and should equal roughly one half of the Young’s modulus (or bulk modulus in the case of fluids) of the material model associated with the SPH particles.

The parameter scale_factor can be used to scale the particles’ contact radii. This can be useful to control how close particles can approach each other. Usually, scale_factor =1.0.

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

No mixing is performed automatically. Currently, no part of USER-SMD supports restarting nor minimization. rRESPA does not apply to this pair style.

## Restrictions

This fix is part of the USER-SMD package. It is only enabled if LAMMPS was built with that package. See the Build package doc page for more info.