Yikes. Li and I have been running some binding curves of H2. Thing is, they don't look like the binding curves of H2 that either John or Lucas published in their papers. The dips of our curves are located around zero separation.
But the dips of those published figures are around 2-something! A conundrum!
Lucas set me straight, like always. By, as he says, going back to basics. The regular DFT calculations don't include nuclear-nuclear repulsion. So, when you calculate the electronic density, the atoms are fixed. If you add in the nuclear-nuclear repulsion term, then you get the dip at a higher number. This is where the molecule was bound if we did a calculation where the nuclei were allowed to move around.
These turn out to be accurate (depending on what flavor of DFT you use), but that's exactly what we're trying to fix! Trying to calculate these properties can help with a lot things like climate models and other things! Yay!