From these dielectric function (ε e,ω) calculations (e.g., Abinit, VASP, etc.), the complex refractive index m ω (= n ω + i κ ω, n ω : refraction index and κ ω : extinction index) is found, i.e., m ω = ε e,ω = ε e,r,ω + i ε e,c,ω). The surface reflectance R of an ideal surface with normal incident from vacuum or air is given as R = [(n ω - 1) + κ ω ]/[(n ω + 1) + κ ω ]. The spectral absorption coefficient is then found from σ ph,ω = 2 ω κ ω / u ph. The spectral absorption coefficient for various electric entities are listed in the below table.