Quasiparticle energies and dielectric functions of diamond polytypes

Abstract

We perform ab initio many-body Green's function calculations to investigate the quasiparticle energies and optical properties of diamond polytypes that have been predicted to be producible via a pressure-induced structural phase transition from carbon nanotube solids. We find, through quasiparticle band-structure calculations within the GW approximation, that the band gaps of two hexagonal (2H- and 4H-type) polytypes of diamond differ significantly from that of cubic diamond as well as from that of the crystalline sp3 carbon phase with a body-centered-tetragonal structure, called bct C4. We also examine the dielectric functions of three polytypes of diamond (cubic, 2H, and 4H) by employing the GW plus Bethe-Salpeter equation approach. The calculated optical absorption spectra are found to be distinct from each other. The lattice mismatches of carbon layers of these diamond polytypes are very small and the total-energy differences are also small. Our work opens up the possibility of fabricating diamond superlattices with various electronic and optoelectronic properties by utilizing and controlling the different stacking sequences of carbon layers.