perturbation, Particular ordinary differential operators (Dirac, one-dimensional Schrödinger, etc.), Perturbations of ordinary differential equations, Perturbation theories for operators and differential equations in quantum theory, Closed and approximate solutions to the Schrödinger, Dirac, Klein-Gordon and other equations of quantum mechanics, eigenvalue, periodic operator, asymptotic behavior, Selfadjoint operator theory in quantum theory, including spectral analysis