BENCHMARK CALCULATIONS WITH CORRELATED MOLECULAR WAVE-FUNCTIONS .2. CONFIGURATION-INTERACTION CALCULATIONS ON 1ST-ROW DIATOMIC HYDRIDES

Potential energy functions have been calculated for the electronic gro und states of the first row diatomic hydrides BH, CH, NH, OH, and HF u sing single- (HF+1+2) and multi-(GVB+1+2 and CAS+1+2) reference intern ally contracted single and double excitation configuration interaction (CI) wave functions. The convergence of the derived spectroscopic con stants and dissociation energies with respect to systematic increases in the size of the one-particle basis set has been investigated for ea ch method using the correlation consistent basis sets of Dunning and c o-workers. The effect of augmenting the basis sets with extra diffuse functions has also been addressed. Using sets of double (cc-pVDZ) thro ugh quintuple (cc-pV5Z) zeta quality, the complete basis set (CBS) lim its for E(e), D(e), r(e), and omega(e) have been estimated for each th eoretical method by taking advantage of the regular convergence behavi or. The estimated CBS limits are compared to the available experimenta l results, and the intrinsic errors associated with each theoretical m ethod are discussed. The potential energy functions obtained from GVB1+2 and CAS+1+2 calculations are observed to yield very comparable spe ctroscopic constants, with errors in D(e) ranging from 0.4 kcal/mol fo r BH to 2.9 kcal/mol for HF. The contraction errors associated with th e internally contracted multireference CI have also been calculated fo r each species; while found to increase from BH to HF, they are, in ge neral, small for all calculated spectroscopic constants. For the cc-pV DZ basis sets, spectroscopic constants have also been determined from full CI calculations.