BENCHMARK CALCULATIONS WITH CORRELATED MOLECULAR WAVE-FUNCTIONS .6. 2ND-ROW-A(2) AND FIRST-ROW 2ND-ROW-AB DIATOMIC-MOLECULES

Benchmark calculations employing the correlation consistent basis sets of Dunning and co-workers are reported for the following diatomic species: Al 2, Si2, P2, S2, Cl2, SiS, PS, PN, PO, and SO. Internally contracted multireference configuration interaction (CMRCI) calculations (correlating valence electrons only) have been performed for each species. For Cl2, P2, and PN, calculations have also been carried out using Møller-Plesset perturbation theory (MP2, MP3, MP4) and the singles and doubles coupled-cluster method with and without perturbative triples [CCSD, CCSD(T]. Spectroscopic constants and dissociation energies are reported for the ground state of each species. In addition, the low-lying excited states of Al2 and Si2 have been investigated. Estimated complete basis set (CBS) limits for the dissociation energies, De, and other spectroscopic constants are obtained from simple exponential extrapolations of the computed quantities. At the CBS limit the root-mean-square (rms) error in De for the CMRCI calculations, the intrinsic error, on the ten species considered here is 3.9 kcal/mol; for re the rms intrinsic error is 0.009 Å, and for ωe it is 5.1 cm-1. © 1994 American Institute of Physics.