Simulation packages developed at Marian group

1. Lattice Kinetic Monte Carlo (LKMC) Simulator (with Chen-Hsi Huang)

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The LKMC simulation package can be used to study microstructural evolution of metal alloys
under various scenarios, including annealing and irradiation. The code uses a primitive lattice
reconstruction to construct FCC, BCC, and HCP rigid crystal lattices. Diffusion is
simulated by way defect-mediated atomic transport. The LKMC simulation package includes
transport by both vacancy and interstitials. We have used it to study alloy evolution in
Fe-Cu, Ni-Au, and W-Re. The code is written in C++.
To know more about the details of the code please see the file.

2. Stochastic Cluster Dynamics (SCD) Simulator (with Chen-Hsi Huang)

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The SCD simulation package contains a computer code written in C used to study the evolution
of defect and solute clusters under the mean-field approximation using a stochastic solver.
The code can be used to study multispecies condtions such as under fusion irradiation including
transmutation. The present parameterization is for the W-Re alloy but we have used the code for
W-He, Fe-Cr, and Fe-He-H.

3. A two-dimensional implementation of a diffuse interface polycrystal plasticity model with grain boundary evolution (with Nikhil Admal)

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This package contains a 2D COMSOL implementation of a diffuse-interface polycrystal plasticity
model with grain boundary evolution demonstrating coupled grain boundary motion, grain rotation and
sliding, and dynamic recovery as described in our paper .

4. MS-STEM-FEM package for multi-slice scanning transmission electron microscopy simulations (with Nick Julian)

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MS-STEM-FEM is a multi-slice scanning transmission electron microscopy (STEM) simulation tool with integrated routines to simulate fluctuation electron microscopy (FEM) experiments as they are performed in a STEM mode microscope. The FEM measurement provides a method of distinguishing between completely disordered and partially ordered materials, but is sensitive to material thickness as explored in our paper . Written in C++ and parallelized with MPI, MS-STEM-FEM scales linearly with model thickness, enabling STEM-FEM simulations using models of the same thicknesses as measured experimentally and an improved ability to relate atomic models and experimental measurements of glassy materials.

5. Three dimensional kinetic Monte Carlo code for screw dislocation-solute interactions in W-Re and W-O (with Yue Zhao)

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Screw dislocation motion in body-centered cubic (bcc) metals is a thermally activated process controlled by kink-pair nucleation. Similarly, solute diffusion in a bcc lattice is generally also thermally activated, consisting of first-nearerst neighbor lattice jumps. To properly investigate dislocation-solute interactions, one has to treat both processes within the same framework. The best such framework is kinetic Monte Carlo (kMC), where events are sampled with the correct probability and time is advanced using an exponential distribution. As described in our paper, these interactions can result in hardening, softening, or both, depending on temperature and solid concentration. The figure above shows the strain rate-temperature map where dynamic strain ageing is observed in W-O, i.e. dislocaion-solute coevolution. The red region delimits the space where solutes and dislocations evolve on similar time scales. The dashed lines in the figure represent thermally activated transitions into the DSA region, each with its own activation energy. The code package is written in C++ and based on the first version of the KMC by Alexander Stukowski (which can also be released upon request).

6. Three dimensional raytracing Monte Carlo code for calculations of secondary electron emission and sputtering in complex geometries (with Andrew Alvarado and Iris Chang)

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Real material surfaces are never perfectly flat. Moreover, particle irradiation can result over time in significant morpohological changes that create roughness and structure. Hence, methods that can capture surface evolution as surfaces are irradiated are needed for morphology predictions. As described in our paper, raytracing Monte Carlo coupled to surface mesh evolution provides an ideal platform to study irradiation of arbitrary surface geometries, such as the microfoam structure shown in the figure. The package linked here contains a raytracing module that simulates single particle ray interactions with discrete surface elements of a given mesh. These interactions are determined according to the phsyics of electron--matter or ion-matter interactions (as described here), which are characterized using scattering Monte Carlo simulations. Lastly, a mesh evolution module gives the time behavior of the structure if and when appropriate.