▎ 摘　　要

This paper gives a theoretical formulation of the electromagnetic response of the quasi-two-dimensional crystals suitable for investigation of optical activity and polariton modes. The response to external electromagnetic field is described by current-current response tensor Pi(mu nu). calculated by solving the Dyson equation in the random phase approximation, where current-current interaction is mediated by the photon propagator D-mu nu. The irreducible current-current response tensor Pi(0)(mu nu). is calculated from the ab initio Kohn-Sham orbitals. The accuracy of Pi(0)(mu nu). is tested in the long-wavelength limit where it gives correct Drude dielectric function and conductivity. The theory is applied to the calculation of optical absorption and conductivity in pristine and doped single-layer graphene and successfully compared with previous calculations and measurements.