GW quasiparticle band structure of CaB6

Much controversy is aroused in the electronic structure of hexaborides both in theories and experiments. In order to settle this problem, the quasiparticle energies are calculated including the effects of electron correlations beyond the local density approximation in the stoichiometric calcium hexaborides. It is shown that electron correlation does not open the band gap, contrary to the naive expectation. This semimetallic band structure coincides with the magnetic oscillation measurements, and the origin of this abnormal quasiparticle shifts is elucidated as being closely connected with the details of the wavefunctions in the non-local interaction terms.