The development of the physical principles underlying novel materials to power the technological needs of the modern world is dependent on having a detailed knowledge of the electronic and structural properties of these materials. First-principles electronic structure theory methods are used here to calculate the structural and electronic properties of complex functional materials with an eye toward applications in artificial photosynthesis and "Beyond Moore's Law" information technology. The details of the methods employed are discussed in Chapter 2.
Artificial photosynthesis, the photocatalytic conversion of water and carbon dioxide into solar fuels such as hydrogen gas and hydrocarbons, is a critical technology for future green energy applications. There are numerous challenges to be overcome in the development of high performing photocatalyst materials. Here, first-principles calculations are used to understand and tune the electronic structure of complex materials for artificial photosynthesis catalysis, in particular ternary metal oxides and layered two-dimensional materials.
- In Chapter 3 we present the results of an experimental collaboration investigating n-type FeWO4 as a high photovoltage photoanode material. We perform electronic structure calculations to shed light on the potential mechanism driving this high photovoltage.
- In Chapter 4 we perform absolute band edge energy calculations on a series of MoS_{2(1-x)}Se_{2x} alloys to corroborate the results obtained from experimental collaborators. We find that the band edges of these alloys can be tuned between the band edges of pristine MoS2 and those of pristine MoSe2 when the alloys assume certain crystal structures. We identify one form of these alloys that does not behave as expected upon incorporation of Se into MoS2 and perform a deeper analysis of the properties of these systems.
- In Chapter 5 we study the effect that biaxial in-plane and uniaxial out-of-plane strain have on heterostructures of monolayer Janus WSSe and monolayer ZnO, both polar materials. We find that the absolute band edges of these heterostructures can be tuned to higher and lower energies via application of different types of strain.
Quantum information is a broad field that encompasses novel ways of storing information, both via beyond-transistors forms of storing binary quantities and via quantum computing. Here, first-principles calculations are performed to study two-dimensional materials for use in valleytronics and in tunable exchange bias.
- In Chapter 6 we develop general design principles for maximizing valley splitting in transition metal dichalcogenides (TMDs) via magnetic substrates. We perform a systematic analysis of the effects of proximity, alignment, and magnetic moment of the magnetic ions in a magnetic substrate and the degree to which these factors affect the magnitude of the calculated valley splitting. We then develop a superexchange model to rationalize these calculated values and elucidate the mechanism driving valley splitting in TMDs via magnetic substrates.
- In Chapter 7 we study the magnetic ordering of a novel, layered metal-organic framework that our experimental collaborators found to exhibit tunable exchange bias. Our calculations support the experimental results indicating that this material is a frustrated antiferromagnet and is a spin glass at low temperatures.
Finally, an overview and outlook are provided in Chapter 8.
