Therefore, in the case of Ca-sc, 𝜒̅ 𝐶𝑎 is the average electron energy of Ca in the sc structure; 𝜒̅ 𝐶𝑎,𝑣𝑎𝑐 is the average atomic electron energy calculated for an isolated atom of Ca and 𝜒̅ 𝐶𝑎 0 is the electronegativity value of Ca as tabulated by , and equal to 6.1 eV/e . To be noted, ∆𝜒̅ 𝐶𝑎 is calculated accounting for all the electrons of Ca, while 𝜒̅ 𝐶𝑎 0 (6.1) refers to the electronegativity of the valence electrons only. Therefore, it is assumed that ∆𝜒̅ 𝐶𝑎 accounts principally for the variation of the valence electron energy, as explained in . TB-LMTO calculations, using the Cs-sc structural parameters at 40 GPa, were performed using the Vosko Wilk Nusair, exchange-correlation potential, plus Perdew-Wang non-local exchange-correlation . Scalar relativistic effects were included. The basis set consisted of spd LMTOs on the Ca atoms and sp LMTOs on the empty spheres (positions of the ISQs to account for the Ca basis-set polarization). The calculations utilized a 25x25x25 mesh in the tetrahedron k-space integrations. The version of the NMTO program employed is not self-consistent and requires the output of the self-consistent potential from the TB-LMTO program. The occupied bands obtained with the full NMTO basis set yielded bands that were in good agreement with those calculated with VASP-R 2 SCAN with the 10 valence electrons POTCAR.