SEARCH Articles Figures Tables Configuration interaction frozen core approximation Encaged atoms frozen-cage approximation Frozen Gaussian approximation Frozen core approximation, combination with Frozen density approximation Frozen environment approximation Frozen molecule approximation, hydrogen Frozen orbital approximation Frozen-cage approximation Frozen-core approximation Frozen-core approximation correlation Frozen-nuclei approximation Frozen-orbital approximation excitation energies Photoionization frozen-cage approximation Space frozen core approximation Spin-free frozen-core approximation The Frozen-Core Approximation