ABSTRACT
This paragraph introduce the basic notions of solid-state physics required the calculation of the electronic structure . It should first be remembered that it is possible to treat the motion of electrons by quantum mechanics and the motion of nuclei by classical mechanics (Born-Oppenheimer approximation) . We shall neglect cou pling between the vibration of nuclei and the motion of electrons (dectron-phonon coupling) on which our analysis will be centred (Ashcroft and Mermin , 1 97 6a) .
