(5as) Developing the Link Between Atomic Level Structure and Macroscopic Properties

Continuous advancements in computational power and efficiency have significantly expanded the system sizes that may be simulated using high accuracy quantum mechanical calculations. I have used density function theory (DFT) to provide further insight into two areas of interest in modern day chemical engineering, electronics and surface chemistry. In particular, I have focused on understanding the role atomic structure plays within the pyrochlore systems (A₂B₂O₇), which have received significant attention for use in high-permittivity dielectrics, capacitors, and high-frequency filter applications. The highly flexible structure allows for incorporation of a wide selection of A and B cations. There is a need to understand the effect of local atomic structure and dynamics on the macroscopic properties to enable rational design within the large range of possible chemical compositions. Through DFT, I have explained the development of atomic displacements within bismuth titanate (Bi₂B⁴⁺₂O₇) and examined the role of chemical substitutions on the local geometric and electronic structure within more technologically relevant bismuth pyrochlores such as Bi_3/2M²⁺Nb_3/2O₇ and Bi_3/2M²⁺Ta_3/2O₇ with M²⁺ = Zn, Mg. I have connected my DFT results with available experimental data to provide further explanation of the role atomic substitutions and structure on the material properties.

My other area of interest is surface chemistry. I have collaborated with Dr. Jason Weaver's experimental group in the investigation of adsorption of simple molecules on polar and non-polar surfaces of SrTiO₃. Specifically, I have examined the role of surface termination and coverage on the favorability of molecular and dissociative adsorption of NH₃ and H₂O. These two molecules serve as simple analogs of a broad range of alcohol and amine reactions that can occur on the oxide surface. The goal of the computational study is to map the effect of local surface structure on the adsorption and reactive behavior observed in ultrahigh vacuum surface science experiments. These two areas of interest have provided an opportunity to simultaneously understand the underlying principles of condensed matter physics and surface science and to collaborate directly with experimentalists within these areas.