In recent years, density functional theory (DFT) calculations have played a crucial role in the expansion of f-element chemistry through contributing to the discovery of newly accessible metal oxidation states and novel electronic structures for lanthanide (Ln) and actinide (An)-containing species. With the purpose of maintaining and extending the utility of such computational approaches, this thesis discusses a few recent applications of DFT towards the characterization and theoretical prediction of new Ln and An-based species. A DFT methodology based on (meta)-generalized gradient approximation (mGGA) density functionals, triple-ζ quality basis sets for metal atoms, and effective core potentials (ECPs) is shown to provide a physical justification for the existence of fully linear Dy and Tb-based metallocene species, Dy/Tb(CpiPr5)2 . This methodology furthermore predicts the stability of linear An-based metallocenes, which was later found to guide synthetic efforts towards the experimental isolation of U(CpiPr5)2, the first An-based “ferrocene” analog. This thesis concludes by highlighting the prediction of EPR parameters, such as the hyperfine coupling constant, electronic g-tensor, and quadrupole coupling constant using DFT for the characterization of newly discovered Ln-based molecular spin qubit systems. An implementation of these quantities is presented within the relativistic exact two-component theory (X2C) method, and benchmark calculations on transition metal and f-element complexes are provided to evaluate choice of the relativistic Hamiltonian, basis set, and density functional approximation (DFA). A recommended set of parameters based on the results of these benchmarks is subsequently presented, and future directions for improving the method are assessed.