Electronic Structure of Ca, Sr, and Ba under Pressure

The electronic-band structure of Ca, Sr, and Ba has been calculated for the fcc phase, in the case of Ca and Sr as a function of atomic volume up to 60% compression. A few preliminary results for the bcc phase are given for comparison. The potential for the calculation was set up with the model potential of Abarenkov, Animalu, and Heine, with the nonlocal terms calculated exactly in the screening and in the matrix elements. The band structure, which is basically nearly-free-electron-like, does not have the simple form of $\mathrm{sp}$ bands near the Fermi level, but is dominated by the admixture of $d$ components there. The fcc phase does not become a semiconductor at small atomic volumes, as has previously been suggested, but becomes a semi-metal because of a line of degeneracy between the lowest two bands which is split only by spin-orbit coupling.