First-principles study of electron-phonon coupling in hole- and electron-doped diamonds in the virtual crystal approximation

The electronic structure, lattice dynamics, and the electron-phonon coupling (EPC) in hole (p)-doped and electron (n)-doped diamonds have been extensively investigated using ab initio methods with the virtual crystal approximation. The calculations of p-doped diamond correctly reproduced all the essential properties of B-doped diamond such as the increase of lattice constant and the redshift of the Raman spectrum with increasing dopant concentration, and the pressure-induced decrease of T-c. The analysis of the spectral function for p-type diamond has shown that optical phonon modes dominate the EPC. From the theoretical prediction of n-doped diamond, it is indicated that the metallic n-doped diamond might be a good superconductor. It is found that the lambda in n-doped diamond increases with the dopant concentration, resulting from the softening of optical phonon modes and the increase of density of states at Fermi level. At a doping level > 2%, the lambda in n-doped diamond is higher than that in p-doped diamond. Phonon linewidth and frozen phonon calculations in n-doped diamond suggested that the longitudinal optical phonon mode contributes mainly to the EPC. The possible mechanism of the predicted superconductivity in n-doped diamond has been discussed.