Accuracy of the Faddeev Random Phase Approximation for Light Atoms

The accuracy of the Faddeev random phase approximation (FRPA) method is tested by calculating the total and ionization energies of a set of light atoms up to Ar. Comparisons are made with the results of coupled-cluster singles and doubles (CCSD), third-order algebraic diagrammatic construction [ADC(3)], and with the experiment. It is seen that even for two-electron systems, He and Be-2+, the inclusion of RPA effects leads to satisfactory results and therefore it does not over-correlate the ground state. The FRPA becomes progressively better for larger atomic numbers where it gives about 5 mH more correlation energy and it shifts ionization potentials by 2-10 mH, with respect to its sister method ADC(3). The corrections for ionization potentials consistently reduce the discrepancies with the experiment.