where the energy levels ε c (1, 0) and ε v (1, 0) correspond to a full core-hole calculation (n c = 0 and n v = 1), whereas ε c (1/3, 2/3) and ε v (1/3, 2/3) are obtained from a calculation with n c = 2/3 and n v = 1/3. In the early days of molecular DFT calculations, the GSTM approach showed promising accuracy of ∼ 0.3 eV for K-shell electron binding energies, although this was later shown to benefit from some error cancellation with the functionals available at the time. Other GSTM schemes involving different fractional occupancies have been proposed more recently, and we have evaluated some of them using a modern slate of approximate XC functionals. Some of these approaches are tested here for XAS.