Describing the\nDisulfide Bond: From the Density Functional\nTheory and Back through the “Lego Brick” Approach

Selected molecular species containing the disulfide bond,\nRSSR,\nhave been considered, these ranging from hydrogen disulfide, H<sub>2</sub>S<sub>2</sub> (R = H), to diphenyl disulfide with R = C<sub>6</sub>H<sub>5</sub>. The aim of this work is two-fold: (i) to investigate\ndifferent computational approaches in order to derive accurate equilibrium\nstructures at an affordable cost, (ii) to employ the results from\nthe first goal in order to benchmark cheaper methodologies rooted\nin the density functional theory. Among the strategies used for the\naccurate geometrical determinations, the semiexperimental approach\nhas been exploited in combination with a reduced-dimensionality VPT2\nmodel, without however obtaining satisfactory results. Instead, the\nso-called “Lego brick” approach turned out to be very\neffective despite the flexibility of the systems investigated. Concerning\nthe second target of this work, the focus was mainly on the S–S\nbond and the structural parameters related to it. Among those tested,\nPBE0(-D3BJ), M06-2X(-D3) and DSD-PBEP86-D3BJ have been found to be\nthe best-performing functionals.