Intrinsic Errors in Several ab Initio Methods: The Dissociation Energy of N2

摘要: Using sequences of correlation consistent basis sets, complete set (CBS) limits for the dissociation energy D{sub c} N{sub 2} have been estimated a variety commonly used electron methods. After extrapolation to CBS limit, difference between theory and experiment corresponds error intrinsic chosen theoretical method. Correlated wave functions (valence electrons correlated only) which errors include internally contracted multireference configuration interaction (CMRCI), singles doubles coupled cluster with without perturbative triple excitations [CCSD, CCSD(T)], second-, third-, fourth-order Moller-Plesset perturbation (MP2, MP3, MP4). For CMRCI CCSD(T), converges smoothly from below experimental value yields smallest errors, -0.8 -1.6 kcal/mol, respectively. In contrast, MP2 MP4, exhibits fortuitously good agreement small sets but leads that are 11.6 3.4 kcal/mol larger than experiment, Correlation 1s core is predicted yield less 1 while those MP4 increase still further. 38 refs., fig., tab.