Quantum corrections to the semiclassical quantization of a nonintegrable   system
  We study the semiclassical behaviour of a two--dimensional nonintegrable system. In particular we analyze the question of quantum corrections to the semiclassical quantization obtaining up to the second order of perturbation theory an explicit analytical formula for the energy levels, which is the usual semiclassical one plus quantum corrections. We compare the "exact" levels obtained numerically to the semiclassical levels studying also the effects of quantum corrections. 
Luca Salasnich and Marko Robnik (CAMTP, University of Maribor,   Slovenia)