First principles study on optical response of graphene oxides: From reduced graphene oxide to the fully oxidized surface

The electronic structure and linear optical properties of oxygen-functionalized graphene are investigated by means of density functional theory (DFT). Our calculations show that oxygen atoms are chemisorbed on the graphene plane and each oxygen atom bonds with two carbon atoms to form a three-membered epoxide group. For different oxygen coverages ranging from 2% to 50% (O/C ratio), the most favorable configurations are calculated. In order to calculate the linear optical response of the structures, the dielectric tensor is derived within the random phase approximation (RPA). Dielectric function, absorption coefficient, optical conductivity, loss function, reflectivity and the refraction index are calculated for both inplane (p) and perpendicular (s) polarizations of the electric field of the incident light. The calculations are performed in the infrared (only the electronic contributions), visible (VS) and ultraviolet (UV) regions and show different characteristic features depending on the degree of oxidation. The optical spectra are anisotropic along the two polarizations of the electric field of the incident light. (C) 2015 Elsevier B.V. All rights reserved.