Solutions lecture 7

src/7_tight-binding_model_sol.md

-# Solutions for lecture 7 exercises
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-### Exercise 1: Lattice vibrations
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-1.
-Hint: Normal modes have the same function as $$\mathbf{e}_1,\mathbf{e}_2,\mathbf{e}_3$$ in $$\mathbb{R}$$.
-Hint: The lectures concerns atom vibrations