Born-Oppenheimer approximation for a harmonic molecule
  We apply the Born--Oppenheimer approximation to a harmonic diatomic molecule with one electron. We compare the exact and approximate results not only for the internal degrees of freedom but also for the motion of the center of mass. We address the problem of the permutation symmetry of identical nuclei and discuss other applications of the model and its limitations. 
Francisco M. Fern\'andez