In an inverse approach, the local potential is determined up to an arbitrary constant. Thus, in principle, the absolute values of the orbital energies are not defined. However, if the correct asymptotic condition on the potential is satisfied, which also sets the constant, then ε H = -I is obtained, where I is the experimental ionization energy, if an exact density is given (row 1 Table ). Similarly, a good approximation to the experimental -I is expected if a good approximation to the density is given from a DFA calculation (row 1 in Table ). However, the corresponding LUMO energy has not been shown to relate to the ionization energy and is not a good approximation to the experimental -I, as discussed in contribution (2.2.16). In atomic calculations, the unoccupied-orbital energies, {ε a }, obtained from inverse Kohn-Sham calculations, have been shown to represent electronic excitations, with ε aε H describing excitation energies of the system with the same number of electrons. Using ε aε H to approximate excitation energies for molecules is less successful.