The Alkaline Earth Metals
The elements of the second column of the periodic Table, known as the alkaline earths, are characterized by a full s shell. The two lighter of them, Be and Mg, crystallize in the hcp structure, Ca and Sr are fcc, and Ba and Ra are bcc. The total energy calculations predict the correct ground state for all of them. For Mg, Sr, and Ba the calculations are based on Hedin-Lundqvist LDA exchange and correlation, while for Be, Ca, and Ra the GGA form was used. The GGA gives lattice constants closer to the experimental values. Be has a very low value of N(EF). Ca and Sr have very similar energy bands i.e., free-electron-like occupied states and d states above EF. Their main difference is in the value of N(EF) which is fairly high for Ca and practically zero for Sr, suggesting semi-metallic behavior. Finally, Ba and Ra resemble Cs in the shape of the energy bands and DOS.