A simple method, based on a plasma oscillations theory of solids, is proposed for the calculation of homopolar ($E_h$) and heteropolar ($C$) energy gaps of ionic crystals having rocksalt structures. We find that $E_h=K{\left(\hslash {\omega }_p\right)}_C^{1.6533}$ eV and $C=K_{1}b{\left(\hslash {\omega }_p\right)}_C^{\frac{2}{3}}\exp [-K_2{\left(\hslash {\omega }_p\right)}_C^{\frac{-1\mathrm{}}{3}}]$ eV, where $K=0.0321\mathrm{}$, $K_1=9.7798\mathrm{}$ and 6.5198 for $A^{\mathrm{I}}{B}^{\mathrm{VII}}$- and $A^{\mathrm{II}}{B}^{\mathrm{VI}}$-type compounds, respectively, and $K_2=7.2239\mathrm{}$. Our calculated values are in excellent agreement with the values reported by different workers.

• Received 2 February 1984

DOI:https://doi.org/10.1103/PhysRevB.29.6993