Understanding f-element spectroscopy by disentangling competing electronic interactions

The optical properties of lanthanide and actinide complexes emerge from a delicate balance of electron interactions, relativistic effects, and the surrounding chemical environment. Understanding how these contributions change across the f-block is important for interpreting spectroscopy and connecting measured signals to electronic structure.

Studvick, Popov, and Celis-Barros used ADF and ligand field density functional theory (LFDFT) to investigate a series of f⁷ lanthanide and actinide ions across different ligand environments. By systematically separating electron-electron repulsion, spin-orbit coupling, and ligand-field effects, the calculations provide a molecular-level picture of how each contribution shapes low-lying excited states and spectroscopic behavior.

The study shows how the balance between these interactions evolves with the identity and oxidation state of the metal and with its ligand environment. In particular, relativistic effects and state mixing become increasingly important in the actinides, while changes in the ligand field connect shifts in electronic structure with changes in metal-ligand covalency.

Beyond these individual systems, the work demonstrates how relativistic electronic-structure modeling can complement spectroscopy by separating effects that are difficult to disentangle experimentally. The authors also highlight LFDFT as a practical route for studying complex f-element electronic structures, providing access to trends in excited states, bonding, and ligand-field interactions at a computational cost suitable for comparing a broader range of systems.