SEARCH Articles Figures Tables An Approximate Second-order Perturbation Treatment Approximation methods second-order energy) Approximations error orders Approximations higher-order modes Approximations of Higher Order Atoms higher-order approximations Boltzmann equation first-order approximation Bond order approximation Bond order approximation, definition Born approximation, zeroth-order Convergence order finite difference approximations Crude Born-Oppenheimer approximation first-order derivatives Determination of Spectra from Viscoelastic Functions Using First-Order Approximations First-Order Regular Approximation First-Order Regular Approximation method First-order absorption models approximation with First-order approximation First-order approximation differential equations First-order approximation, relaxation First-order approximation, relaxation spectra First-order polarization propagator approximation Fourth-order, generally approximations Hamiltonian Zeroth-order regular approximation Hamiltonian infinite-order regular approximation Hamiltonians zeroth-order regular approximation Hartree-Fock approximation zeroth-order Hamiltonian High-Order Compact (Hermitian) Current Approximation Higher Order Approximation Techniques Higher order approximation Higher-order orbital approximations Higher-order orbital approximations configurations Higher-order phase integral approximation Hydrogen molecule zero-order approximation Infinite order sudden approximation IOSA) Infinite-Order Regular Approximation Infinite-order sudden approximation Matrix first-order approximation Order of approximation Pseudo-first order approximation Reactive infinite-order sudden approximate Reduced-order models approximation errors Rotational Infinite Order Sudden Approximation Second order polarization propagator approximation Second-Order Polarization Propagator Approximation model Second-order Polarization Propagator Approximation Calculations Second-order approximation, constrained Second-order approximation, time-dependent Second-order approximation, time-dependent transfer Second-order approximations Second-order ladder approximation Second-order perturbation theory approximate Second-order regular approximation Steady states first-order approximation Subject zero-order approximation The Electronic States of Atoms. III. Higher-Order Approximations Third-order approximations Third-order polarization propagator approximation Wave functions, approximate correct zeroth-order Zero-Order Regular Approximation Zero-Order Regular Approximation model Zero-order approximation Zero-order approximation excited state Zero-order approximation ground state Zero-order approximation probability density Zero-order approximation, natural Zero-order regular approximation ZORA) Zeroth order regular approximation for relativistic effects Zeroth-order approximation Zeroth-order approximation calculation Zeroth-order approximation states Zeroth-order approximations construction Zeroth-order polarization propagator approximation Zeroth-order regular approximation Zeroth-order regular approximation (ZORA Zeroth-order regular approximation Hamiltonian/method Zeroth-order regular approximation energies/results Zeroth-order regular approximation method