# fix nve/superquadric command

## Syntax

    fix ID group-ID nve/superquadric keyword value

- ID, group-ID are documented in fix command
- nve/superquadric = style name of this fix command
- zero or one keyword/value pair may be appended to args; the dim keyword must be used
- keyword = integration_scheme

    integration_scheme values = 0, 1 or 2
      0 = based on Richardson iterations
      1 = symplectic algorithm (recommended)
      2 = leap-frog predictor-corrector
      3 = Woodem scheme

## Examples

    fix 1 all nve/superquadric integration_scheme 1

## Description

Perform constant NVE integration to update position, velocity, orientation, and angular velocity for superquadric particles in the group each timestep. V is volume; E is energy. This creates a system trajectory consistent with the microcanonical ensemble.

This fix differs from the fix nve/sphere command, which assumes point particles and only updates their position and velocity.

This model is used in the framework of SUPERQUADRIC simulations. For more information see also the `SUPERQUADRIC guide`.

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

No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during `energy minimization`.

## Restrictions

This fix requires atom_style superquadric.

All particles in the group must be finite-size. They cannot be point particles, but they can be aspherical/spherical as defined by their shape attribute.

## Related commands

fix nve, fix nve/sphere

## Default

integration_scheme = 1

( `Miller <http://scitation.aip.org/content/aip/journal/jcp/116/20/10.1063/1.1473654>`_ ) Miller. et al., Journal of Chemical Physics, 116 (20), p 8649-8659 (2002)

( `Walton <http://www.grainflow.com/index_files/Rotary_Drum_Simulation_DOE-NSF-1993.pdf>`_ ) Walton and Braun, DOE/NSF Workshop on Flow of Particulates and Fluids, p 1-18 (1993)