Relativistic and quantum electrodynamics effects on NMR shielding tensors of Tl$X$ ($X$ = H, F, Cl, Br, I, At) molecules

Abstract

Results of relativistic calculations of nuclear magnetic resonance shielding tensors ($\sigma$) for the thallium monocation (Tl$^+$), thallium hydride (TlH) and thallium halides (TlF, TlCl, TlBr, TlI, and TlAt) are presented as obtained within a four-component polarization propagator formalism and a two-component linear response approach within the zeroth-order regular approximation. Additionally, some quantum electrodynamical (QED) effects on those NMR shieldings are estimated. A strong dependence of $\sigma$(Tl) on the bonding partner is found, together with a very weak dependence of QED effects with them. In order to explain the trends observed, the excitation patterns associated with relativistic $ee$ (or paramagnetic-like) and $pp$ (or diamagnetic-like) contributions to $\sigma$ are analyzed. For this purpose, also the electronic spin-free and spin-dependent contributions are separated within the two-component zeroth-order regular approximation, and the influence of spin-orbit coupling on involved molecular orbitals is studied, which allows for a thorough understanding of the underlying mechanisms.