Vol 3 - Landau, Lifshitz - Quantum mechanics - non-relativistic theory (3ed., 1991) · Problem 38.1
Perturbation Theory
Physics — Landau & Lifshitz · perturbation-theory-eigenfunctions-second-order
Perturbation Theory
Physics — Landau & Lifshitz · perturbation-theory-eigenfunctions-second-order