SEARCH Articles Figures Tables Comparison of the Variation and Perturbation Methods Method, perturbational Perturbation at an Atom in the Simple Hiickel MO Method Perturbation by Paramagnetic Species, the Oxygen Pressure Method Perturbation method Perturbative methods The Scope and Methods oF Perturbation Theory The magnetic field perturbation method (MFP) Time-Dependent Perturbation Theory The Sum over States Method