Energy bands cesium chloride

Valence energy bands for cesium chloride in (a) the simplest LCAO approximation and... 

If, on the other hand, the bands of cesium chloride were as in Fig. 2-2,b, the eight electrons of each chlorine cesium atom pair would fill the states only to the energy [ shown in the figure this is called the Fermi energy. Each band would only be partly filled, a feature that, as we shall see, is characteristic of a metal. 

Valence energy bands for cesium chloride in (a) the simplest LCAO approximation and (b) in the nearly-free-electron limit. Parameters e, b, V2, etc., are chosen for convenience and are not realistic. 

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