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Unformatted text preview: Solid State Theory Exercise 2 FS 11 Prof. M. Sigrist Point groups and their representations Exercise 2.1 Energy bands of almost free electrons on the fcc lattice Let us consider almost free electrons on a facecentered cubic (fcc) lattice. The goal of this exercise is to compute the lowest energy bands along the Δline using degenerate perturbation theory and the machinery of group theory . Remember that in reciprocal space, the fcc lattice transforms into a bodycentered cubic (bcc) lattice. The point group of the cubic Bravais lattices (simple cubic, fcc, bcc) is denoted by O h (symmetry group of a cube). Its character table is given in Tab. 1. a) We first study the Γ point ( ~ k = 0). For free electrons ( V = 0) the lowest energy level is nondegenerate and the second one has an eight fold degeneracy. We focus on the second level and denote the eightdimensional representation of O h defined on this subspace by Γ. Find the irreducible representations contained in Γ. Compute the group character...
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This note was uploaded on 10/04/2011 for the course PHYS fs11 taught by Professor Sigrist during the Spring '11 term at Swiss Federal Institute of Technology Zurich.
 Spring '11
 Sigrist
 Energy

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