Ab initio potential energy curves, transition dipole moments and spin–orbit coupling matrix elements for the first twenty states of the calcium dimer§

Abstract

State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the calcium diatom in the Born–Oppenheimer approximation for the first twenty singlet and triplet states dissociating into 3P+1S, 3D+1S, 1D+1S and 1P+1S atomic states. All the excited state potential curves were computed using a combination of the linear response theory within the coupled-cluster singles and doubles framework for the core–core and core–valence electronic correlation with the full configuration interaction for the valence–valence correlation. The electric and magnetic transition dipole moments governing the X and X, respectively, have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Spin–orbit coupling matrix elements have been evaluated within the complete active space self-consistent field framework using an effective core potential from the Cowan–Griffin relativistic ab initio model potential method. With these couplings, the spin–orbit coupled potential energy curves for the and 1 u states of the calcium diatom have been obtained. Our results are compared with other ab initio calculations and with the experimental data available for the calcium diatom. §Dedicated to Professor Andrzej J. Sadlej on the occasion of his 65th birthday.