Dynamic and static behavior of the E-E bonds (E, E′ = S and Se) in cystine and derivatives, elucidated by AIM dual functional analysis

Atoms-in-molecules dual functional analysis (AIM-DFA) is applied to the E-E' bonds (E, E' = S and Se) in R-cystine (1) and the derivatives of 1, together with MeEE'Me. H-b(r(c)) are plotted versus H-b(r(c)) = V-b(r(c))/2 at bond critical points (BCPs), where H-b(r(c)) = V-b(r(c))/2 = (h(2)/8m)del(2) rho(b)(r(c)). The plots are analyzed by the polar coordinate (R, theta) representation. Data of perturbed structures around the fully optimized structures are also plotted in this treatment. Perturbed structures are generated using NIV (normal coordinates of internal vibrations). Each plot for an interaction with data of a fully optimized and four perturbed structures gives a curve, which supplies important information. It is expressed by (theta(p), k(p)): theta(p) corresponds to the tangent line for the plot measured from the y-direction and k(p) is the curvature. While (R, theta) correspond to the static nature of interactions, (theta(p), k(p)) represent the dynamic nature. The behavior of the E-E' bonds is well described by (R, theta) and (theta(p), k(p)).