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Abstract
Structural and dielectric properties of a variety of materials are studied through a combinationof Monte Carlo and Langevin dynamics simulations. A computational methodology is developed
using the bond-charge model and suitable multi-body potentials to recreate the frequency dependent
dielectric function ϵ(ω) of correlated materials. Simple harmonic potentials for atom/bond-charge
and atom/atom bond-length interactions are used in combination with harmonic three-body potentials
for atom/atom/atom bond-angle interactions. Langevin dynamics simulations at 300K are performed
to recreate the dielectric spectra of pristine SiO2, MoS2, and SmNiO3 to which we compare with
ellipsometry measurements. Dielectric modulation of SmNiO3 due to oxygen vacancies is then
investigated through modelling the vacancy/free-charge interaction through a Lennard-Jones (12-6)
potential. With this modelling scheme, we were able to reproduce experimental trends from s-SNOM
measurements of oxygen vacant samples. Proceeding similarly as before, we model the dopant
dynamics of H+ doped NdNiO3 with a combination of harmonic bond-length and bond-angle
interactions. Doing so recreates dielectric reconstruction seen in s-SNOM measurements of doped
samples. Utilization of more complex three-body dopant interactions is corroborated by DFT
studies of the same materials, providing insight into the role of multi-body interactions in such
samples. Finally, we explore novel structural phenomena seen in twisted bilayer MoS2. We make
use of the Stillinger-Weber (4-0) potential to model the intra-layer interactions, and Lennard-Jones
potentials for inter-layer interactions. We observe characteristic corrugation and domain formation
commensurate with DFPT and experimental studies of similar heterostructures. We then show
displacement fields at different twisting angles to compare with DFT calculations with which we
have a high level of agreement. The global and local dielectric function are then calculated as we
remark about shifts in Im(ϵ). We then introduce vacancies in the sample and calculate the dielectric
spectra, to which we see again peak shifting in Im(ϵ) towards lower energy correlated with a
decrease in total corrugation of the system. We conclude with showcasing several structures arising
from various choices of interaction parameters and remarking at their complexity and variety.