The open-shell coupled-cluster method: Ionization potentials and electron affinities of the alkali atoms, Li to Cs

The open-shell coupled-cluster method with single and double excitations (CCSD) is applied to the alkali atoms, Li to Cs, with moderately large basis sets. The calculated electron affinities are all within 0.01 eV of experiment, with valence-shell correlation contributing almost all the correction to the (poor) Hartree-Fock results. Errors in the ²S ionization potentials range from 0.02 (Li) to 0.22 eV (Cs); with relativistic corrections estimated from numerical Hartree-Fock, IPs are within 0.1 eV of experiment. ²P IPs are even more accurate (0.02-0.04 eV).