Rayleigh-Schrödinger Perturbation Theory

Rayleigh-Schrödinger Perturbation Theory is a mathematical approach used in quantum mechanics to solve problems involving complex systems that cannot be solved exactly. When a small change, or "perturbation," is introduced to a known system, this theory helps us calculate how the properties of the system (like energy levels) change. It starts with the exact solution of the unperturbed system and gradually incorporates the effects of the perturbation to provide an approximate solution, which is particularly useful in understanding complex atomic and molecular interactions.