Role of dG(b)(r(c))/dw and dV(b)(r(c))/dw is revealed as the basic atoms-inmolecules (AIM) functions to evaluate, classify, and understand the nature of interactions, as well as G(b)(r(c)) and V-b(r(c)). The border area between van der Waals (vdW) adducts and hydrogen-bonded (HB) adducts is shown to appear at around dG(b)(r(c))/dw = -dV(b)(r(c))/dw and that between molecular complexes (MC) and trigonal bipyramidal adducts (TBP) of chalcogenide dihalides appears at around 2dG(b)(r(c))/dw = -dV(b)(r(c))/dw. H-b(r(c)) are plotted versus H-b(r(c)) - V-b(r(c))/2 at bond critical points (BCPs) in the AIM dual functional analysis. The plots incorporat2e)1.3121 classification of interactions by the signs of del(2)rho(b)(r(c)) and H-b(r(c)). R [= (x(2) + y(2))(1/2) corresponds to the energy for the interaction in question at BCPs, where (x, y) = (H-b(r(c)), H-b(r(c)) - V-b(r(c))/2) and (x, y) = (0, 0) at the origin. The segment of lines for the plots (S) should correspond to energy, if the segment is substantially linear. The first derivative of S (dS) is demonstrated to be proportional to R. Relations between AIM functions, such as dV(b)(r(c))/dw, dG(b)(r(c))/dw, dH(b)(r(c))/d[H-b(r(c)) - V-b(r(c))/2], d(2)V(b)(r(c))/dw(2), d(2)G(b)(r(c))/dw(2), and d(2)H(b)(r(c))/d[H-b(r(c)) V-b(r(c))/2](2), are also discussed. The nature of interactions. results help us to understand the