CALCULATION OF THE ELECTRON-AFFINITIES OF THE 2ND ROW ATOMS - AL-CL

The electron affinities (EAs) of aluminum though chlorine have been ca lculated with multireference single and double excitation configuratio n interaction calculations (MRSD-CI) with the augmented correlation co nsistent basis sets of Woon and Dunning V. Chem. Phys. 98, 1358 (1993) ]. The orbital space for the complete active space (CAS) wave function s is systematically expanded beyond the Hartree-Fock wave function by inclusion of additional s, p, and d orbitals. This approach provides a well balanced treatment of the neutral and ionic charge states and le d to accurate EAs for hydrogen and the first row atoms [R. A. Kendall, T. H. Dunning, Jr., and R. J. Harrison, J. Chem. Phys. 96, 6796 (1992 )]. The best MRSD-CI values for the EAs (in eV) of the second row atom s are Al, 0.440; Si, 1.413; P, 0.689; S, 2.023; and Cl, 3.606. Inclusi on of spin-orbit effects in the calculated EAs yields (experimental va lues in parentheses): Al, 0.437 (0.441); Si, 1.395 (1.385); P, 0.700 ( 0.746); S, 2.019 (-2.0771; and Cl, 3.570 (3.613). The amenability of t he correlation consistent basis sets for extrapolating to the complete basis set limit has also been exploited in this work. The neutral and anion energies are extrapolated separately in order to account for th e different convergence rates in the energies of the two species. The extrapolated values of the EAs, including an empirical spin-orbit corr ection, are Al, 0.438; Si, 1.395; P, 0.713; S, 2.047; and Cl, 3.596. A dditional calculations suggest that the remaining error is a measure o f the residual imbalance in the MRSD-CI treatments of the neutral and anion. Extrapolated EAs for the first row atoms are also reported.