An essential element of actinide-based research is the prediction of the stability and properties of actinide-containing compounds. Since their acute toxicity, radioactivity, and instability complicate experimental studies on actinide compounds, theoretical approaches have to be used to determine their properties and reactivity. Unfortunately, conventional computational models are difficult, primarily because the computational resources required grow unfavourably with the size of the system, an effect known as the curse of dimension. Thus, innovative new approaches must be developed that break the curse of dimension. One such approach describes molecules as a collection of noninteracting electron pairs, called geminals. Conventional geminal-based methods developed so far are, however, inappropriate for actinide chemistry. The main objective of this project is, thus, to extend geminal-based models to be applicable to actinide chemistry. To accomplish this task, we need to include (i) computationally efficient ways to account for relativistic effects, (ii) correlations between electrons beyond electron-pairing effects, (iii) the modeling of electronically excited states, and (iv) the description of unpaired electrons. The developed models should be robust, computationally cheap, reliable, and black-box-like, requiring minimal user-software interplay. These technical advantages compared to standard approaches will facilitate theoretical modeling of actinide-containing materials out of reach of present-day quantum chemistry methods and will be of crucial importance for a fundamental understanding of actinide chemistry. For instance, the extended geminal models will provide the essential insights that are needed to guide the synthesis of new actinide compounds that can be used to separate Uranium and Plutonium from the other components in the soup of nuclear waste. Furthermore, the scope of applications of the proposed new quantum mechanical model can be easily extended to other areas of chemistry and material physics like lanthanide and transition-metal chemistry, biochemical reactions, and semiconductor physics.
Our numerical studies demonstrate that all new quantum mechanical methods that have been developed in this project provide an improved, atomistic, and quantitative computational model to describe actinide chemistry. In general, our methods outperform all conventional quantum mechanical approaches used in computational chemistry that are suitable for actinide-containing compounds, while simultaneously the computational scaling could be significantly reduced. To conclude, the proposed geminal-based models are a robust, computationally inexpensive, and user-friendly alternative to standard, more complicated computational approaches.
