The quasiparticle properties of a technologically important material ${\mathrm{Ca}}_2\mathrm{Si}$ is studied by means of the all electron GW approximation based on the projector-augmented-wave method (PAW). Both the orthorhombic and the cubic phases are explored, and the resulting band structures are compared with those obtained in the framework of the local-density approximation (LDA) of the density functional theory. An improved energy band gap for both phases of this material is compared to experiment. The dielectric function is also computed for both phases, and its shown that the quasiparticle self-energy correction and the local-field effects strongly affect the optical spectra and the static dielectric function. The analysis of the locations of the Brillouin zone $\mathbf{k}$ points and the interband transitions responsible of the main peak is conducted for both phases.

• Received 8 March 2005

DOI:https://doi.org/10.1103/PhysRevB.72.085103