First principles insights into material and molecular properties: environmental and actinide chemistry applications

Computer simulations offer unique atomic-level insights into the chemical reactions which control the behavior of different materials and molecules. Incorporation of these simulations into research is particularly important in the fields of environmental and nuclear chemistry. Environmental processes are controlled by complex reactions occurring between solid-state minerals and aqueous molecules. As these minerals and molecules make up the common nutrients, contaminants, and soils in our environment, understanding their interactions is key to identifying the everyday processes which make up the Earth. Experimental techniques developed to explore these reactions can have limitations due to reaction complexity, thus, examining these systems computationally may further bridge the gap in knowledge. Alternatively, the field of nuclear chemistry looks to study the behavior of the actinide elements. Actinides are becoming increasingly used for energy production, weapons development, waste management, and medicinal applications. Each of these elements are radioactive, while some rapidly decay and can only be artificially made in small amounts. Therefore, extreme care must be used when performing experiments on these systems, making computational modeling of these species especially important as it can help reduce the risks involved in their handling.

In this thesis, computational models are used to study interactions occurring naturally in the environment and between actinide elements. The first few research chapters examine the reactions of two common minerals with aqueous oxyanion and organic molecules. The work mainly develops new methods to accurately predict the energetics which control how minerals and molecules behave towards each other. Accurate predictions of these interactions can further the understanding of how contaminants and nutrients are transported in the environment, and help develop applied areas of science, such as the purification of drinking water and cleaner soils for agriculture. The later research chapters then explore two actinide elements (uranium and neptunium) engaged in interactions with themselves and various other molecules. The research mainly explores uranium and neptunium in their aqueous states and predicts how experiments may be used to monitor and then control these interactions. As the production of nuclear energy leads to highly radioactive waste involving both uranium and neptunium, this research will be important for the future development of waste recycling and storage for a cleaner and safer environment.