# Origin of band Gap

I know that in the Kronig Penney model there are values of the energy $E$ for which solutions to the Schrodinger equation don't exist. I understand that these forbidden values of $E$ form the band gaps. How, intuitively, does the crystal structure lead to the existence of forbidden bands?

• I tried to improve the wording of your question a bit because it wasn't clear how this question is different from the one you posted yesterday (physics.stackexchange.com/q/153539). – DanielSank Dec 16 '14 at 18:50