Oganesson is a Semiconductor:On the Relativistic Band‐Gap Narrowing in the Heaviest Noble‐Gas Solids.

: Oganesson (Og) is the most recent addition to Group 18. Investigations of its atomic electronic structure have unraveled a tremendous impact of relativistic effects, raising the question whether the heaviest noble gas lives up to its position in the periodic table. To address the issue, we explore the electronic structure of bulk Og by means of relativistic Kohn-Sham density functional theory and many-body perturbation theory in the form of the GW method. Calculating the band structure of the noble-gas solids from Ne to Og, we demonstrate excellent agreement for the band gaps of the experimentally known solids from Ne to Xe and provide values of 7.1 eV and 1.5 eV for the unknown solids of Rn and Og. While this is in line with periodic trends for Rn, the band gap of Og completely breaks with these trends. The surprisingly small band gap of Og moreover means that, in stark contrast to all other noble-gas solids, the solid form of Og is a semiconductor.