Recent Developments in Perturbation Theory

摘要: Publisher Summary The purpose of this chapter is to provide information on the recent developments in perturbation theory. In years, there a great increase interest application theory fundamental problems quantum chemistry. Perturbation designed deal systematically with effects small perturbations physical systems when are mathematically too difficult calculate exactly, and properties unperturbed system known. new applications have been mainly atoms where reciprocal atomic number, l/Z, provides natural parameter. These may be divided into two groups. first consists calculations energy levels, outgrowth Hylleraas's classic work 1/Z expansion for two-electron atoms. second group calculation expectation values other molecules, much more origin. There principal reasons success these applications: (1) sufficient accuracy frequently obtained from knowledge first-order perturbed wave function, (2) advantage that functional form function shaped by itself.