SEARCH Articles Figures Tables Energy second Intermolecular perturbation second-order energy Moller-Plesset perturbation theory second-order energy derivatives NMR Parameters Defined as Second-Order Energy Perturbations Ordering energy Perturbation energy Perturbation order Perturbed energy Rayleigh-Schrodinger perturbation theory, second order energy Second-order energy Second-order vibrational perturbation theory energy levels