Spectroscopic quality ab initio potential curves for CH, NH, OH and HF. A convergence study

A calibration study has been carried out on the ground-state potential curves of CH, NH, OH and HF. Using uncontracted spdfgh or spdfghi basis sets in conjunction with treatments of core correlation and imperfections in the CCSD(T) method, r(e) and omega(e) of the first-row diatomic hydrides can on average be reproduced to within 0.0002 Angstrom and 1 cm(-1), respectively, as can the first 4-6 vibrational quanta. The CCSD(T) basis set limit systematically overestimates omega(e) by 4-9 cm(-1) and underestimates r(e) by 0.0003-0.0006 Angstrom. Higher anharmonicities exhibit pronounced basis set sensitivity, which is markedly reduced upon uncontracting the basis set. (C) 1998 Elsevier Science B.V. All rights reserved.