Remark on the correlation between the refractive index and the optical band gap in some crystalline solids

The correlation between static refractive index (ns) and optical band gap (Eg) based on the Wemple-DiDomenico (WD) model and the empirical correlation between the energy of an effective dispersive oscillator and optical band gap is examined for 52 crystalline solids. A comparison with two recently published empirical relationships between ns and Eg indicates that the use of the WD model provides better results and, more importantly, connects the ns versus Eg dependence with some chemical characteristics of solids such as the coordination number of cation, the valence of anion, the effective number of valence electrons and ionicity.