Einstein–Brillouin–Keller method

The Einstein–Brillouin–Keller (EBK) method is a semiclassical technique (named after Albert Einstein, Léon Brillouin, and Joseph B. Keller) used to compute eigenvalues in quantum-mechanical systems. EBK quantization is an improvement from Bohr–Sommerfeld quantization which did not consider the caustic phase jumps at classical turning points.

Source: Wikipedia — Einstein–Brillouin–Keller method (CC BY-SA 4.0)