The Chemistry of Heavy Elements: Probing Relativistic Chemical Bonding

Abstract

The bottommost part of the periodic table has a unique chemistry, where the high velocities of the inner-shell electrons prevent their description by the usual Schrödinger equation. The resulting so-called relativistic effects have numerous chemical implications, on both macro and microscale, ranging from physical properties to reactivity. However, experimental probes on these intriguing atoms are limited by their natural availability and, more importantly, the danger associated with their radioactivity. Quantum chemical calculations, on the other hand, face the challenge of far more complex algebra, which demands substantial computational resources. Relativistic Hamiltonians, which act over all electrons in the system, are currently among the most accurate methods used to describe the electronic structure of heavy atoms. Over the years, the Normalized Elimination of the Small Component (NESC) Hamiltonian, originally proposed by Dyall, has been extensively improved by the CATCO group; the latest version, NESC with atomic unitary transformation (NESCau), allows for accurate calculations on large systems at a reasonable cost. In this dissertation, we applied the NESC and NESCau Hamiltonians, paired with the well-established theories of local vibrational mode analysis (LMA) and quantum theory of atoms in molecules (QTAIM), to describe chemical bonding in heavy atoms. Our results showcase intriguing aspects of the chemistry of uranium and lanthanides, including their geometry, bonding mechanisms, and chemical affinities