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[tex]\frac{P}{ka}[/tex]sin(ka)+cos(ka)=cos(qa)

(a is the period of the potential)

Since the expression on the right-hand side of the equation takes only values between -1 and 1, and the function on left-hand side might get values outside this range, energy gaps (and "energy bands") are created.

So this is a good description of the energy of an electron in a periodic potential. But is this description relevant to all solids? In conductors there is no forbidden gap between the valence band and the conduction band; In semiconductors there is a gap but it's relatively small, and in insulators this gap is relatively large. Does that mean that the difference between these situations is the parameter "P" in the equation above?

Thanks:shy: