It is evident that such a sharp step-like increase in the dispersion energy is unphysical and is an inadvertent consequence of the design of the D3 method itself. Before delving into the specific reasons for this behavior, let's first consider other D-type corrections (Figure ). As observed from the graph, both D3(BJ) and D3(0) illustrate that the damping function only affects the size of the step (with D3(0) having a smaller step size than D3(BJ) by approximately 2.5 kJ/mol), but the step appears at the same distance of ~1.65 Å. Notably, the D4 correction also exhibits this kind of artifact, though the step is shifted toward shorter distances. In this particular case, this shift prevents the D4 method from falling into the H2-NiKur-(2) geometry. However, due to the unphysical behavior of the dispersion energy close to the true local minimum, it is very problematic to obtain the correct Hessian for H2-NiKur-(1) with the D4 correction turned on. Importantly, the D2 correction does not have this artifact, and the dispersion energy does not exhibit sharp changes in the considered region. It is worth noting that the magnitude of this artifact (but not the position) also depends on the functional used. The most pronounced effects are seen with the GGA BLYP functional (which is effectively dispersionless, and so lightly damped), while the more strongly damped M06-2X functional (which captures some medium-range correlation) shows almost negligible step size. Since the (much simpler) D2 correction does not exhibit the same problems as D3 and D4, the reasons for the artifact might lie in the different definitions of the C6 coefficients employed in these models. While the D2 model uses a single unchanged C6 AB coefficient value for each atomic pair AB, the D3 and D4 schemes have C6 AB coefficients that depend on the CN of the atoms in the pair (Equations 6,7). Thus, the issue may arise if the CN A or the C6 AB coefficients change sharply in the problematic region. After evaluating the CN of Ni, we found that it changes rather smoothly without any sharp transitions (Figure ) along the H2-Ni distance. However, the C6 values do indeed change sharply with slight variations in CN. The illustrative relative C6 AB vs. CN A graphs are given in Figure .