Exploring the Influence of (n$-$1)d Subvalence Correlation and of Spin-Orbit Coupling on Chalcogen Bonding

Abstract

This article presents a comprehensive computational investigation into chalcogen bonding interactions, focusing specifically on elucidating the role of subvalence (n$-$1)d and (n$-$1)sp correlation. The incorporation of inner-shell (n$-$1)d correlation leads to a decrease in interaction energies for chalcogen-bonded systems (at least those studied herein), contradicting the observations regarding halogen bonding documented by Kesharwani et al. in \textit{J. Phys. Chem. A}, \textbf{2018}, 122 (8), 2184-2197. The significance of (n$-$1)sp subvalence correlation appears to be lower by an order of magnitude. Notably, among the various components of interaction energies computed at the PNO-LCCSD(T) or DF-CCSD levels, we identify the PNO-LMP2 or DF-MP2 component of the (n$-$1)d correlation as predominant. Furthermore, we delve into the impact of second-order spin-orbit coupling (SOC2) on these interactions. \markNM{The SOC2 effects appear to be less significant than the (n$-$1)d correlation; however, they remain non-trivial, particularly for Te complexes. For the Se complexes, SOC2 is much less important.} Generally, SOC2 stabilizes monomers more than dimers, resulting in reduced binding of the latter. Notably, at equilibrium and stretched geometries, SOC2 and (n$-$1)d destabilize the complex; however, at compressed geometries, they exhibit opposing effects, with (n$-$1)d becoming stabilizing.