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.