Nano foam atomistic configuration generated using the SolutionRasterizer.

Mesoscale microstructure simulations using the phase field method can be utilized to generate initial structures for large sacle molecular dynamics simulations. One application is the construction of nano-foam atomistic samples from simulations of spinodal decomposition.

MOOSE provides a built in system to template an atomic coordinate file in the .xyz format from the simulation result in a given mesh file. The workflow is as follows

1. Set up a phase field simulation and output a finite element mesh file
2. Create a bulk .xyz input file with the desired underlying lattice and crystal structure
3. Use the minimal input file shown below to load the mesh and .xyz input

MOOSE will load the .xyz input and finite element mesh superpose both and use thresholding to carve out rejected atoms while retaining accepted atoms. Finally a new .xyz output is written containing only the accepted atoms, generating a porous microstructure.

## SolutionRasterizer

Doxygen

The SolutionRasterizer user object is derived from the SolutionUserObject and inherits its input parameters. It takes the following additional input parameters:

Input Parameter Description
xyz_input An .xyz file as an input file. This input file should contain an atomistic simulation cell completely filled with atoms of a chosen crystal structure (a polycrystalline sample can be supplied).
xyz_output Output file containing the filtered (or mapped) atomic coordinate file.
raster_mode = FILTER In FILTER mode the SolutionRasterizer uses thresholding on a specified non-linear variable to reject or accept atom from the input file to pass to the output .xyz file.
raster_mode = MAP In MAP mode the SolutionRasterizer takes the atoms from the input file and add an additional column to the data set containing the value of a specified non-linear variable.
threshold Value of the selected non-linear variable to use in FILTER mode used to accept or reject atoms from the xyz_input file.

### Minimal working input file

The following input can be executed with the MOOSE Phase Field module executable and will

• load the mesh file diffuse_out.e
• load the atomic coordinate file in.xyz
• accept all atoms at the coordinates where the value of the non-linear variable c is above a value of 0.5
• write out the atomic coordinate file out.xyz
[Mesh]
type = GeneratedMesh
dim = 3
[]

[Problem]
kernel_coverage_check = false
solve = false
[]

[Executioner]
[]

[UserObjects]
[./soln]
type = SolutionRasterizer
system_variables = 'c'
mesh = diffuse_out.e
execute_on = timestep_begin

variable = c
xyz_input = in.xyz
xyz_output = out.xyz

# raster_mode = MAP
raster_mode = FILTER
threshold = 0.5
[../]
[]