\(\renewcommand{\AA}{\text{Å}}\)

# fix smd/adjust_dt command

## Syntax

    fix ID group-ID smd/adjust_dt arg

- ID, group-ID are documented in fix command

- smd/adjust_dt = style name of this fix command

- arg = s_fact

      s_fact = safety factor

## Examples

    fix 1 all smd/adjust_dt 0.1

## Description

The fix calculates a new stable time increment for use with the SMD time integrators.

The stable time increment is based on multiple conditions. For the SPH pair styles, a CFL criterion (Courant, Friedrichs & Lewy, 1928) is evaluated, which determines the speed of sound cannot propagate further than a typical spacing between particles within a single time step to ensure no information is lost. For the contact pair styles, a linear analysis of the pair potential determines a stable maximum time step.

This fix inquires the minimum stable time increment across all particles contained in the group for which this fix is defined. An additional safety factor s_fact is applied to the time increment.

See this PDF guide to use Smooth Mach Dynamics in LAMMPS.

## Restart, fix_modify, output, run start/stop, minimize info

Currently, no part of MACHDYN supports restarting nor minimization.

## Restrictions

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

## Related commands

smd/tlsph_dt

## Default

none