Evaluation of two-centre dipole matrix elements of Slater s, p and d orbitals; application to the optical absorption spectrum of NbS2monolayers

The authors present a numerical method to evaluate two-centre electric dipole matrix elements involving Slater s, p and d orbitals. This allows them to develop a convenient method to compute optical properties of metallic materials for which the tight-binding band structure is available. The method is believed to be particularly useful in the case of highly anisotropic materials where arguments based purely on the joint densities of states will fail. An application is presented to a NbS2 monolayer. They find that the calculated optical anisotropy is sensitive to the choice of Slater orbital screening length, while the frequency dependence of the transition probability for a given direction of polarisation is less sensitive to the choice of parameters.