In this work, we take a revision of perturbation theory in Quantum Mechanics and we were shown that Rayleigh-Schrodinger perturbative series did not converge to exact numerical results of anharmonic oscillator or Stark effect in Hydrogen atom. We utilize Pade approximants, as a technique of renormalization of perturbative energies. We treat fourth order perturbation to anharmonic oscillator lambdax4 and verify the accuracy of Pade approximants in relation to numerical exact solution.
stationary perturbation theory; Pade approximants
