Formally exact quantization condition for nonrelativistic quantum   systems
  Based on the standard transfer matrix, a formally exact quantization condition for arbitrary potentials, which outflanks and unifies the historical approaches, is derived. It can be used to find the exact bound-state energy eigenvalues of the quantum system without solving an equation of motion for the system wave functions. 
Yong-Cheng Ou, Zhuang-Qi Cao, and Qi-Shun Shen