where 𝑛 𝑖 is the number of electrons having energy 𝜀 𝑖 , and 𝑖 runs over all the occupied states. This corresponds to the integral, up to the Fermi level 𝜀 𝑓 , of all the density of states (DOSs) multiplied by the energy of the states. In the case of Ca-sc, there is only one atom in the unit cell, therefore, the total electron energy density 𝑋 also corresponds to the atomic electron energy density 𝑋 𝐴 . Then, the average atomic electron energy 𝜒̅ 𝐴 is calculated dividing 𝑋 𝐴 by the total number of electrons explicitly treated for the atom 𝐴, 𝑛 𝐴 , which equals to 20 for Ca.