Inverse Versus Normal Behavior of Interactions, Elucidated Based on the Dynamic Nature with QTAIM Dual-Functional Analysis

In QTAIM dual-functional analysis, H(b)(r(c)) is plotted versus H(b)(r(c)) − V(b)(r(c))/2 for the interactions, where H(b)(r(c)) and V(b)(r(c)) are the total electron energy densities and potential energy densities, respectively, at the bond critical points (BCPs) on the interactions in question. The plots are analyzed by the polar (R, θ) coordinate representation for the data from the fully optimized structures, while those from the perturbed structures around the fully optimized structures are analyzed by (θ(p), κ(p)). θ(p) corresponds to the tangent line of the plot, and κ(p) is the curvature; θ and θ(p) are measured from the y-axis and y-direction, respectively. The normal and inverse behavior of interactions is proposed for the cases of θ(p) > θ and θ(p) < θ, respectively. The origin and the mechanism for the behavior are elucidated. Interactions with θ(p) < θ are typically found, although seldom for [F–I-∗-F](−), [MeS-∗-TeMe](2+), [HS-∗-TeH](2+) and CF(3)SO(2)N-∗-IMe, where the asterisks emphasize the existence of BCPs in the interactions and where [Cl–Cl-∗-Cl](−) and CF(3)SO(2)N-∗-BrMe were employed as the reference of θ(p) > θ. The inverse behavior of the interactions is demonstrated to arise when H(b)(r(c)) − V(b)(r(c))/2 and when the corresponding G(b)(r(c)), the kinetic energy densities at BCPs, does not show normal behavior.