A long-standing misinterpretation of the origin of the conduction band in sodium chloride is corrected. We show that this band is primarily derived from chlorine states, and not from sodium states as is generally believed. The anion character of the conduction band holds for the other alkali halides as well. The reinterpretation of this band clarifies why the size of the band gap in these insulators does not depend on the alkali metal in a first-order approximation.
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The weak dependence on the cation is due to the size of the cation which affects the lattice parameter and therefore also the width of bands, and to the slight hybridization of the anion states in the conduction band with cation s states at higher energies—and for K, Rb, and Cs with cation d states as well.
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© 1999 American Association of Physics Teachers.
1999
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