Summary of Research Group’s Activities

The Materials Modeling Group at Northern Kentucky University uses computer simulation methods to study point defects and diffusion in crystalline materials. The group has studied both ceramic and metallic materials, but recent efforts have focused on intermetallic compounds with funding support from the National Science Foundation (RUI: Search for Verifiable Complex Diffusion Mechanisms, grant number DMR 15-08189). Intermetallic compounds are used throughout industry with applications in fields ranging from medicine to defense. A key to developing new, improved intermetallic materials is developing a better fundamental understanding of how atomic-scale defects affect materials properties and how atoms move in these compounds. Research activities in this group are divided into two projects: use of computer simulations (1) to predict defect and diffusion properties in intermetallic and other crystalline materials and (2) to help interpret data obtained from a class of experimental techniques called hyperfine methods.

Modeling Atomic-Scale Processes in Crystalline Materials

Energy minimization and molecular dynamics techniques are used to calculate defect formation, association, and migration energies. Results of these simulations are combined with thermodynamic models and theories of atomic diffusion to predict diffusion properties and defect-induced changes in materials properties. Two models for interactions are used, depending on the length- and time-scales of the simulation: density functional theory for the electronic scale and empirical potentials (e.g., the second nearest neighbor modified embedded atom method) for the atomic scale. Commercially available software is used for these simulations.

Software

VASP (https://www.vasp.at/). Available at UK and licensed to Zacate & his research group.
Wien2k (http://www.wien2k.at/). Licensed to Zacate & his research group.
GULP (http://gulp.curtin.edu.au/gulp/). Licensed to Zacate & his research group.
LAMMPS (https://lammps.sandia.gov/). GNU General Public License.

Researchers (all non-UK)

Faculty member: Matthew Zacate (NKU)

Students:

Chadwick Evans

Daniel Franklin

David Maess (NKU)

Simulations of Stochastically Fluctuating Hyperfine Interactions

A class of experimental techniques known as hyperfine methods measure interactions between tracer nuclei and extranuclear electromagnetic fields (the hyperfine interaction). This set of methods can be used to study, as examples, magnetic structure and atomic-scale symmetry-breaking caused by point defects in crystalline materials. If measured interactions fluctuate at a rate comparable to the inverse time-scale of the hyperfine method, spectra will be damped and degree of damping related to the interaction fluctuation rate. In such a case, hyperfine methods can be used to study spin fluctuations and atomic jumps of point defects.

The purpose of this project is to simulate hyperfine spectra in the presence of fluctuating hyperfine interactions using stochastic models customized to describe the physics and chemistry of a problem of interest. This allows prediction of interesting systems to study experimentally, interpretation of experimental results, and, when incorporated with fitting software, determination of measured hyperfine fluctuation rates.

Software

Stochastic Hyperfine Interactions Modeling Library (SHIML) with simulation software developed at NKU. Computer Physics Communications 199, 180-181 (2016) and Computer Physics Communications 182, 1061-1077 (2011). GNU General Public License + private NKU software in development.
Wien2k (http://www.wien2k.at/). Licensed to Zacate & his research group.

Researchers (all non-UK)

Faculty member: Matthew Zacate (NKU)

Detailed group-member information

Matthew Zacate, faculty member at NKU, 7/7/1969

Chadwick Evans, undergraduate student at NKU, 07/25/1994

Daniel Franklin, undergraduate student at NKU, 01/11/1999

David Maess, undergraduate student at NKU, 08/08/1982

Grants:

Publications:

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