Posted by Markus on May 26, 2014, 6:41 pm
Hello, I've encountered problems of this type: A potential can be written as V(r)=V(r+R) where R is a lattice vector. Show that V can be written as V(r)= sum( V_G exp(i G.r) ) While I do understand that if V(r) can be expressed as a Fourier series, we have translational symmetry, I don't know how to proof that any function with translational symmetry can be expressed as a Fourier series. Can you help? 
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