Understanding the reasons for the appearance of the artifact, we can now examine the C6 AB vs. CN plots for other elements to predict other potential ill-behaved cases. Surprisingly, most atomic pairs exhibit sharp changes in C6 AB plots. The most significant problems occur with pairs involving metal atoms, which is predictable since the change in the C6 AB coefficient is substantial (in absolute values, Figure ) when transitioning from a free atom to singly coordinated and then to doubly coordinated atoms, and so on. However, even carbon atoms (which exhibit a smoother C6 behavior) show some rather large jumps between CN C = 1 to 2 and CN C = 3 to 4.