Structural, elastic, electronic and optical properties as well as chemical bonding of the binary alkali metal selenides M 2 Se ( M = Li , Na , K , Rb ) were calculated using the full potential linearized augmented plane method. From the elastic constants it is inferred that these compounds are brittle in nature. The results of the electronic band structure show that Na 2 Se has a direct energy band gap (Γ-Γ), Li 2 Se has an indirect energy band gap (Γ- X), while K 2 Se and Rb 2 Se have an indirect energy band gap (X-Γ). Analysis of the charge distribution plots reveals a dominated ionic bonding in the herein studied compounds. Additionally, we have calculated the optical properties, namely, the real and the imaginary parts of the dielectric function, refractive index, extinction coefficient, optical conductivity and reflectivity for radiation up to 30.0 eV. All these compounds have direct energy band gap greater than 3.1 eV suggesting their use for manufacturing high frequency devices.
No Resistive Normal Electrons in Beginning Superconducting States