ENDOR, the F‐Center Ground State, and Conduction Bands in Alkali Halide Crystals

Although both experiment and theory indicate that the lowest conduction‐band minimum in most alkali halides is at k = 0 , recent theoretical analysis by Grachev, Deigen, and Pekar of ENDOR data on the F ‐center ground state suggests that in KCl and NaF the lowest minima may be away from k = 0 , along the (100) direction. In this paper we discuss the problem of precise calculation of the F‐center ground state and interpretation of ENDOR data. We present the result of a calculation, based on a new local‐orbital approximation to the Hartree‐Fock equations, of the F‐center ground state in KCl. This calculation does not agree in all respects with experimental results. We present a critical analysis of the technique of Grachev et al., and show that if one uses different ENDOR data and a slightly different approach, the case for (100) minima in KCl is considerably weakened.