My lecture notes on condensed matter physics talk about pseudopotentials of atoms where the core electrons are replaced by an effective potential. This is in the context of DFT. In the lecture notes, my lecturer talks about transferability, i.e. the ability of the pseudopotential to work in various atomic configurations. My lecturer proposes a test of the transferability of a pseudopotential in the following way: Devise a series of atomic configurations representing (approximations to) excited states of the atom; then compute the energy difference between them for both the all-electron case and the pseudopotential approximation.
What is it meant by that atomic configurations represent excited states of the atoms? I thought only the electrons could be excited, and there should be different excited states for all configurations. Can you explain what is meant by this?