Relativistic coupled-cluster-based linear response theory for ionization potentials of alkali-metal and alkaline-earth-metal atoms

We have developed and applied the relativistic coupled-cluster-based linear response theory (RCCLRT) for computing the principal as well as the shake- up ionization potentials (IP's) of Li, Be, Na, and Mg where the single-part icle orbitals are generated by solving the relativistic Hartree-Fock-Rootha an equations using the Gaussian basis functions on a grid. The computed pri ncipal and shake-up ionization energies by the RCCLRT approach art: in favo rable agreement with the experimental results. Since for the (one-valence) IP problem, then is a formal equivalence between the principal IP values as obtained from the CCLRT and those obtained as eigenvalues of the multirefe rence coupled-cluster theory, the computed quantities are fully size extens ive. The approach via the RCCLRT has the additional advantage of providing the shake-up IP's as well. These an, however, not fully size extensive, but the error scales as the number of valence excitations (2h-1p), so the inex tensivity error is rather small.