Perturbation theory

Ch 17.1 A method for approximating the eigenstates and eigenvalues of a Hamiltonian $\hat{H} = \hat{H}_0 + \lambda\hat{V}$ when $\hat{H}_0$ is solvable and $\hat{V}$ is "small." Non-degenerate perturbation theory (Ch 17) and degenerate perturbation theory (Ch 18) handle different cases. *See also:*