Multireference Studies of Transition Metal and Actinide Containing Molecular Systems

Density functional theory (DFT) has long been the most widely used method in quantum chemistry for studying kinetics, reaction mechanisms, molecular interactions, and more. However, it faces significant challenges in accurately predicting and describing systems with unpaired electrons, such as radicals and transition metal complexes, i.e., strongly correlated systems. Understanding the properties of such systems often requires quantum chemistry methods beyond DFT, notably multireference wave function approaches. Multireference methods such as complete active space self-consistent field (CASSCF) and second-order perturbation theory (CASPT2) are commonly employed. However, their high computational cost and complexity often limit their applicability to small systems. To address this, new methods have been developed that aim to retain high accuracy while reducing computational demands. One such method, multiconfiguration pair-density functional theory (MC-PDFT), has demonstrated accuracy comparable to the gold-standard CASPT2, but with significantly lower computational expense. This thesis focuses on applying multireference wave function methods, particularly MC-PDFT, to study the magnetic properties of transition metal complexes, including (i) molecular qubits and (ii) newly synthesized molecules.