Relationships between optical band gap and thermodynamic properties of binary oxides

A clear correlation between optical band gaps of oxides and the microscopic energies calculated from standard formation enthalpy or standard free energy related to one oxygen is demonstrated. This result is in agreement with the maximum chemical hardness principle proposed by Pearson (J. Am. Chem. Soc. 1987;64:561; J. Chem. Educ. 1999;76:267) and Parr and Chattaraj (J. Am. Chem. Soc. 1991;113:1854).