The basis-set convergence of singlet and triplet pair energies of coupled-cluster theory including single and double excitations is accelerated by means of extrapolations based on the distinct convergence behaviors of these pairs. The new extrapolation procedure predicts a nonrelativistic Born-Oppenheimer inversion barrier of 1767 ± 12 cm −1 for NH3 .A n effective one-dimensional, vibrationally averaged barrier of 2021 ± 20 cm −1 is obtained when relativistic effects (+20 cm −1 ), Born-Oppenheimer diagonal corrections (−10 cm −1 ), and zero-point vibrations (+244 cm −1 ) are accounted for. c � 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1306-1314, 2001
['Wim Klopper', 'Claire C. M. Samson', 'György Tarczay', 'Attila G. Császár']
Equilibrium inversion barrier of NH3 from extrapolated coupled‐cluster pair energies