T>T: Exact Cusp–Tail Density Functional for the Bound Two-Electron Coulomb Series

My background is in physics and when I entered the weird and wonderful world of chemistry, I remember reading about the Hohenberg and Kohn theorem which has been floating around my head ever since. If you ever see me sitting quietly in a corner, I am probably thinking about this problem, or just staring at the wall but hopefully the former. The TLDR of this theorem is: “the ground-state proper...