Electronic structure and optical properties of rutile RuO₂ from first principles

The systematic trends of electrionic structure and optical properties of rutile (P4₂/mnm) RuO₂ have been calculated by using the plane-wave norm-conserving pseudopotential density functional theory (DFT) method within the generalised gradient approximation (GGA) for the exchange—correlation potential. The obtained equilibrium structure parameters are in excellent agreement with the experimental data. The calculated bulk modulus and elastic constants are also in good agreement with the experimental data and available theoretical calculations. Analysis based on electronic structure and pseudogap reveals that the bonding nature in RuO₂ is a combination of covalent, ionic and metallic bonds. Based on a Kramers—Kronig analysis of the reflectivity, we have obtained the spectral dependence of the real and imaginary parts of the complex dielectric constant (\varepsilon₁ and \varepsilon₂, respectively) and the refractive index (n); and comparisons have shown that the theoretical results agree well with the experimental data as well. Meanwhile, we have also calculated the absorption coefficient, reflectivity index, electron energy loss function of RuO₂ for radiation up to 30 eV. As a result, the predicted reflectivity index is in good agreement with the experimental data at low energies.