Band Structure and Electronic Properties of AgCl and AgBr

A theoretical study of the electronic properties of silver chloride and bromide is reported. The valence bands of AgCl have been calculated by the tight-binding method, using a screened free-electron exchange potential. It is found that the highest valence band has several maxima at points other than $\Gamma$, while the results of experiment and other preliminary calculations indicate that the lowest conduction band is simple, with a minimum at $\Gamma$. The spin-orbit splitting in the highest valence band for the state ${L_3}^{\prime }$ has been computed and is found to be less than 0.05 eV. It is shown that Brown's low-temperature data on optical absorption in the long-wavelength tail can be explained by our band structure and Cole's experimental phonon dispersion curves. Using the AgCl calculation as a starting point, we have analyzed the available optical data on both AgCl and AgBr along lines suggested by the work of Phillips in the alkali halides and rare gases. For both crystals, conduction-band structures are proposed which appear to explain the gross features of the data.