Quasiparticle properties of the possible superconductor materials LiBC and NaBC

The quasiparticle band structures within the GW approximation of the possible superconductors LiBC and NaBC are presented. The GW correction to the LDA is shown to be strongly dependent on the degree of orbital localization, and the overall correction cannot be reproduced by a rigid band shift as in conventional semiconductors. Precise values of the interband transitions for high-symmetry points in the Brillouin zone are given. The imaginary part of the self-energy which is related to the lifetime of quasiparticles, is presented in order to be compared with future experiments. Moreover, the ground-state properties of LiBC and NaBC are studied and it is shown that the bonding is partly covalent.