Nonlinear Oscillator Hamiltonian from Nonlinear Differential Equation   and Calculation of Accurate Energy Levels
  A new method for generating analytical expression of quantum Hamiltonian from non-linear differential equation with stationary energy level has been formulated.Further calculation of energy levels have been carried out analytically using and numerically using matrix diagonalisation method. 
Biswanath Rath and P. Mallick
quant-ph