Optical properties and correlation effects in NaxCoO2 -: art. no. 205103

We have calculated the optical spectra of NaxCoO2 for x=0.3, 0.5, and 0.7 within the local density approximation (LDA). A comparison of our results to available experimental data shows good agreement of the important features and trends, but reveals a nearly uniform shift of peak positions and poor quantitative reproduction of intensities. We show, through application of a simple model, that these differences can be attributed to overhybridization between Co and O orbitals and spin fluctuations that renormalize the bandwidth. Application of the LDA + U procedure shifts the optical peaks farther from their experimental locations, indicating that this method of incorporating correlation effects is ill-suited for the case of NaxCoO2.