Quantum Monte Carlo ground state energies for the singly charged ions from Li through Ar.

Nonrelativistic frozen nucleus all-electron Quantum Monte Carlo ground state energies of positive and negative ions Li(+) to Ar(+) and Li(-) to Cl(-), respectively, are reported. Explicitly correlated wave functions with a single configuration model function times a Jastrow factor are employed for all of the systems studied. The accuracy obtained for the ions in the third period is similar to that reached for the ions in the second one. For those ions with a stronger multiconfiguration nature a restricted multiconfiguration expansion has been employed. The ground state energy here obtained for the charged species shows a similar quality to that reached for neutral atoms. Starting from those results, ionization potentials and electron affinities are calculated.