Perturbation Theory
A set of mathematical approximation methods for finding an approximate solution to a complex problem by starting from the exact solution of a simpler unperturbed problem.
Governing formula
H = H₀ + λ H', E_n = E_n^(0) + λ E_n^(1) + λ² E_n^(2) + ...
SI unit
Approximation Power Series
In depth
Decomposes the system Hamiltonian H into exactly solvable H₀ plus small perturbation λ H'. Expresses energy eigenvalues and wave functions as power series in small parameter λ.
Examples in the real world
Calculating the Zeeman effect and fine structure energy corrections in quantum mechanics.