Dynamic behavior of hydrogen bonds from pure closed shell to shared shell interaction regions elucidated by AIM dual functional analysis.

The dynamic behavior of hydrogen bonds (HBs) was clarified for the wide range of interactions applying AIM dual functional analysis. Plots of H(b)(r(c)) versus H(b)(r(c)) - V(b)(r(c))/2 are analyzed in the polar (R, θ) representation, where H(b)(r(c)) and V(b)(r(c)) are total electron and potential energy densities at bond critical points, respectively, for the fully optimized structures. Data of the fully optimized structure and four perturbed ones around it are plotted for each interaction, which give a specific curve. The curve is analyzed by (θ(p), κ(p)): θ(p) corresponds to the tangent line from the y-direction and κ(p) is the curvature. Whereas (R, θ) correspond to the static nature, (θ(p), κ(p)) represent the dynamic nature of interactions. Indeed, HBs can be classified only by one parameter of θ, but θ(p) supplies more information necessary for better understanding of HBs. Although H(2)Se--HSeH and H(3)N--HNH(2) show the nature of pure CS (closed shell) of the vdW-type, H(2)S--HSH and H(2)O--HOH contain the nature of pure CS other than the vdW-type (HB-typical). The regular CS nature is observed for B--HF (B = HF, H(2)Se, H(2)S, H(2)O, and H(2)C═O). The HF--HF interaction is described as HB-typical, whereas others are by CT(MC)-type. The nature of H(3)N--HX (X = F, Cl, Br) is regular CS of the CT(TBP)-type. HBs in charged species, such as HOH-*-OH and [H(2)O--H-*-OH(2)], show the weak covalent nature of SS (shard shell). The dynamic behavior of HBs helps us to understand HBs in more detail, in addition to the static behavior.