anisotropic command

Warning

GPU support for this command has not been tested and may not work as expected.

Syntax

fix ID group-ID change/size/superquadric/anisotropic keywords values

ID, is documented in fix command.
change/size/superquadric/anisotropic = style name of this fix command
zero or more keyword/value pairs may be appended
keyword = file or file_coords or region or binsize

   file value = filename
     filename = filename for reading particle grow field data (string)
   file_coords value = filename_coords
     filename_coords = filename to write coordinate data of grid cells (string)
   region value = region-ID
     region-ID = ID of region atoms must be in to have added mass

binsize value = bsize
  bsize = size of bins for structured grid used (length units)

Examples

fix grow all change/size/superquadric/anisotropic region reg binsize 0.05 file data/mag.file file_coords data/file.coords

Description

This fix allows anisotropic growing or shrinking of superquadric particles in the fix group.: On one axis a particle could grow while on the other axis it ca shrink.

If the region keyword is used, the atom must also be in the specified geometric region in order to have the mass added to it.

The bounding box of the region defined is used as a basis for the structured grid. Keyword binsize, which is mandatory, is used to define the grid size for this structured grid storing the field information.

With the optional keyword file_coords, you can have the code write the coordinates of each bin / grid cell to a file. An example for a grid just containing 4 cells is shown below:

x   y   z
-0.025  -0.025 0.025
-0.025   0.025 0.025
 0.025  -0.025 0.025
 0.025   0.025 0.025
-0.025  -0.025 0.075
-0.025   0.025 0.075
 0.025  -0.025 0.075
 0.025   0.025 0.075

The mandatory keyword file is used to specify the location of the file containing the field values growing particle. It contains of a header line and data lines. The header line starts with “x y z”, followed by the name of each field and the length of 3. The first 3 columns must contain the coordinate of the bin / grid cell, followed by data for the field growthRate. Sizes of particles in each direction (a, b, c) increase/decrease linearly with time:

a(t)=a(0)+a(0)*t*kx

b(t)=b(0)+b(0)*t*ky

c(t)=c(0)+c(0)*t*kz

where a(t), b(t) and c(t) are the sizes of a particle in x,y,z directions at the moment of time t. Coefficients (kx, ky, kz) are components of growthRate field that defines the relative increase/decrease of a particle size in x,y,z directions during 1s simulation time with respect to initial values a(0), b(0) and c(0),

For example, triplet 0.2 0.0 -0.1 would mean that a particle after 1s of simulation becomes 20% larger in x-direction, no size change in y-direction and 10% smaller in z-direction.

An example for the file format required for this fix is shown here:

x   y   z               growthRate 3
-0.025  -0.025 0.025    -0.3 0.0 0.3
-0.025   0.025 0.025    -0.3 0.0 0.3
 0.025  -0.025 0.025    0.3 0.0 -0.3
 0.025   0.025 0.025    0.3 0.0 -0.3
-0.025  -0.025 0.075    0.1 0.3 0.2
-0.025   0.025 0.075    0.1 0.3 0.2
 0.025  -0.025 0.075    0.1 0.3 0.2
 0.025   0.025 0.075    0.1 0.3 0.2

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. No output is 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.

Restrictions

This fix does not work with fix multisphere This fix requires atom_style superquadric.

Default

region = whole simulation box