 Variational perturbation theory

Variational perturbation theory is a method used in quantum mechanics and statistical mechanics to approximate the properties of a quantum system, particularly when dealing with a Hamiltonian that can be separated into a solvable part and a perturbation. The approach combines elements of perturbation theory with ideas from the variational principle, which is a powerful tool in quantum mechanics for approximating the ground state energy and wave functions of complex systems. ### Key Concepts 1.