Table shows a test of eq. ( ) in which we have calculated 𝜇, and each of its components, for all atoms of the first three rows of the periodic table . In these examples, 𝜒 is approximated as the average energy of occupied Kohn-Sham (KS) orbitals, while the derivatives in eq. ( ) are evaluated through a finite-difference approximation (see the computational details section). The results of eq. ( ) agree near perfectly with the in-practice definition of the Fermi level in computational physics and chemistry: the average energy of the highest occupied and lowest unoccupied (HOMO and LUMO) orbitals. This agreement is significant because the terms of eq. ( ) are all evaluated from occupied electronic states, avoiding the use of virtual orbitals. The root mean square deviation between these two options for estimating 𝜇, or 𝜀 @ , is 0.06 eV.