Spectra of barium, radium, and element 120: Application of the combined correlation-potential, singles-doubles, and configuration-interactionab initiomethods

We apply a version of the recently developed approach combining the correlation-potential, linearized singles-doubles coupled-cluster, and configuration-interaction methods to the spectra of the heavy alkaline earths barium, radium, and element 120. Quantum electrodynamics radiative corrections are included. We have found excellent agreement between ab initio theory and experiment for the spectra of barium and radium, and we make accurate predictions for missing and unreliable data for all three atoms.