fix mixing command

Warning

This command is deprecated, please use calculate mixing_index instead

Syntax

fix ID group-ID mixing every N keywords values

  • ID, is documented in fix command.

  • mixing = style name of this fix command

  • every = mandatory keyword

  • N = calculate the mixing index every this many timesteps

  • zero or more keyword/value pairs may be appended

  • keyword = region

region value = region-ID
  region-ID = ID of region atoms must be in to be evaluated

Examples

fix mix all mixing every 100 region mixregion

Description

This fix computes the GMMI mixing index as defined by Asmar et al. For each atom type i, the GMMI is defined as

GMMIx = x-center of volume of all particle of type i / x-center of volume of all particles

The GMMI is a vector (x/y/z) where the definition above applies to each spatial coordinate. The center of volume is calculated by summing over all eligible particles

x-center of volume = sum_over_all_particles_i (voli*(xi - x_ref)) / sum_over_all_particles_i(voli)

where xi is the x-position of the particle, x_ref is a reference position and voli is the volume of particle i. The same formula applies for the y and z coordinates, accordingly.

The result of the calculation are 3 mixing indices GMMIx, GMMIy and GMMIz. The value range of the GMMI can be interpreted as follows:

GMMI = 0

no data available

GMMI = 1

perfect mixing

0 < GMMI < 1

no perfect mixing (smaller number means worse) particles of type i have lower coordinate than average

1 < GMMI < …

no perfect mixing (larger number means worse) particles of type i have higher coordinate than average

If the region keyword is used, mixing of particles in the specified geometric region is evaluated. x_ref is then equal to the minimum coordinates of the regions bounding box in each direction.

Keyword every has to be used, and defines how often the GMMI is evaluated

Restart, fix_modify, output, run start/stop

This fix does not need to write data to binary restart files. None of the fix_modify options are relevant to this fix. A global array is stored by this fix for access by various output commands. For each particle type in the simulation, it contains the x,y,and z components of the GMMI mixing index as defined above. No parameter of this fix can be used with the start/stop keywords of the run command.

Restrictions

None

Related commands: none

Default: none

(Asmar) B. N. Asmar, P. A. Langston, A. J. Matchett, Granular Matter, December 2002, Volume 4, Issue 3, pp 129-138