Perturbation theory for projected states II. Convergence criteria and a soluble model
B. Atalay, A. Mann, Ronald F. Peierls
Abstract It is shown that a perturbation expansion for projected states proposed earlier satisfies the Schrödinger equation. Modified forms of the series are suggested, and criteria for their convergence are discussed. The method is applied to the ‘Lipkin model' for a two-level many-body problem, which is exactly soluble. The second-order term in the perturbation series is shown to give a good approximation, and is compared with alternative methods. The convergence factor of the series is shown to be better than that of ordinary perturbation theory, which in most cases of this model is divergent.
Proceedings of the Royal Society of London A Mathematical and Physical Sciences•Nov 27, 1973•14 citations