Graduation Term

Spring 2026

Degree Name

Master of Science (MS)

Department

Department of Physics

Committee Chair

Matt Caplan

Committee Member

Neil Christensen

Committee Member

Q. Charles Su

Abstract

Molecular dynamics (MD) simulations are used to explore the microscopic behaviors of complex systems that cannot be easily studied experimentally. In particular, the microphysics of high energy density (HED) astrophysical plasma environments remain inaccessible by modern experiment---even in laser facilities, these plasmas exist only on short timescales that do not lend easily to investigation. The diffusion of point and group defects through crystallized plasmas in the cores of white dwarfs and neutron star crusts, called Coulomb crystals, has potentially macroscopic implications for the evolution of these bodies. Thus, I employ the widely-used MD code LAMMPS to simulate small Coulomb crystal lattices of varying screening and coupling with artificially-introduced defects. By tracking their propagation throughout the crystal, this research shows that interstitial and vacancy jump frequencies follow a clear power-law trend over the dimensionless Coulomb coupling parameter. At high coupling (low temperature), interstitial simulations become restricted to one-dimensional collinear motion that forms a crowdion; however, vacancies do not experience the analogue of this phenomenon. As a result, vacancies continue to exhibit three-dimensional diffusion to much higher coupling than interstitials under the same conditions. These diffusion behaviors may have larger implications for crystals experiencing shear forces, thereby influencing knowledge of the thermal and dynamical evolution of the dense matter within white dwarf cores and neutron star crusts.

Access Type

Thesis-Open Access

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