Is there a physical meaning to the SCF energy of a molecule obtained using pseudopotentials to represent the core electrons of heavy atoms (for example gold)?
I've been running calculations in Gaussian on a system with a number of gold atoms and I became curious whether my use of pseudopotentials for the gold core electrons was skewing the results I obtained. So, I attempted to run a smaller test comparing two identical systems where one used pseudopotentials (specifically the LANL2DZ basis set) for the gold atoms and the other was all-electron with the DZP basis set. When I performed thess calculations, I got very similar orbital energies for the frontier orbitals, but the total energies were completely different, with the total energy of the all-electron calculation approximately 50 times more stable than the pseudopotential calculation (e.g. -100000 vs -2000 au).
Perhaps I've missed some obvious shortfall of pseudopotentials, but I just don't see how the energies obtained could be so different. I would expect an error in the calculation if the orbitals hadn't made sense or there was any unusual messages in the log file, but I didn't notice any such problem. The geometries and route sections used in each case are the same (besides the one having pseudo=read) and the only difference was the basis sets, where LANL2DZ is built in and I found DZP through the basis set exchange.