Valence activity of SO-coupled atomic core shells in solid compounds of heavy elements.

Area of Science:

• Solid-state chemistry
• Quantum chemistry
• Materials science

Background:

• Atomic orbital-energy patterns exhibit chemically relevant changes across light to heavy elements.
• These changes are significant for both fundamental chemical theory and practical material applications.

Purpose of the Study:

• To quantum-chemically investigate the geometric and electronic structures of solid thorium dioxide ([ThO2]) and various uranium trioxide ([UO3]) phases.
• To analyze these structures at a realistic relativistic level, considering the effects of spin-orbit (SO) coupling.

Main Methods:

• Relativistic quantum-chemical calculations were performed.
• Geometric and electronic structures of [ThO2] and [UO3] phases were analyzed.
• The influence of spin-orbit coupling on electronic band structures was examined.

Main Results:

• The smallest band gap was observed for delta-[UO3], characterized by short U-O distances and high Oh symmetry.
• A phenomenon termed "pushing up from below" (PFB) was identified, driven by Pauli-repulsion and covalent mixing involving U(6p) and O(2p) orbitals.
• Significant spin-orbit splitting of the light element's valence band was observed, linked to PFB.

Conclusions:

• PFB and PFB-induced SO splitting, previously unconsidered in solid-state science, have been demonstrated.
• These findings reveal new mechanisms influencing electronic structures in heavy element compounds.
• The study opens avenues for novel electronic material applications based on these principles.