【摘要】 建立了非微扰外推模式下的几种 G3(QCI)方法 :G3(QCI/fu1)、 G3(QCI/fu2)、 G3(QCI/fu1)//B3PW91和 G3(QCI/fu2)//B3PW91.其中 ,电子能量用 QCISD(T,FC)/G3large直接计算 ,芯电子相关能分别在 MP2/6-31G(d)和 MP2/6-311G(d,p)级别上计算 .对 125个 G2-1 test set的计算结果表明 ,总体精度与 G3和 G3//B3LYP相当；平均绝对偏差分别为 4.370、 4.389、 4.061和 4.022 kJ· mol－ 1,相应 G3和 G3 //B3LYP分别为 4.27和 4.05 kJ· mol－ 1.文章提出的方法排除了 G3中外推办法的不确定因素 ,且更适用于非平衡几何构型体系能量的定量计算 .更多还原

【Abstract】 G3(QCI) model chemistry,which eliminates the uncertainties of basis sets and theoretical methods extrapolation approximations,is defined via eq.: E0[G3(QCI)]=E[QCISD(T,FC)/G3large]＋Δ E(full)＋ E(SO)＋ E(ZPE)＋ E(HLC) where the electronic energy E[QCISD(T,FC)/G3large] is directly calculated at QCISD(T,FC)/G3large level,the core electron correlation energyΔ E(full) is calculated at MP2/6-31G(d) (denoted as fu1) or MP2/6-311G(d,p) (denoted as fu2) level and the spin-orbit coupling E(SO) for atomic species is from the experiments as what has been done in the G3[2] theory.Four varieties of G3(QCI) model chemistry theoretical procedure,namely G3(QCI/fu1),G3(QCI/fu2),G3(QCI/fu1)//B3PW91 and G3(QCI/fu2)//B3PW91,are proposed and tested with the G2-1 test set.The E(HLC)′ s have been defined and optimized in the same manner as in G3 theory,which are － 3.024nα－ 5.397nβ on molecules and－ 2.085nα－ 5.636nβ on atomic species for G3(QCI/fu1),－ 3.085nα－ 5.478nβ on molecules and－ 1.885nα－ 5.466nβ on atomic species for G3(QCI/fu2),－ 2.495nα－ 5.478nβ on molecules and－ 1.790nα－ 5.584nβ on atomic species for G3(QCI/fu1)//B3PW91 and－ 2.670nα－ 5.380nβ on molecules and－ 1.923nα－ 5.465nβ on atomic species for G3(QCI/fu2)//B3PW91.The over-all accuracy is close to that of the G3 or G3 //B3LYP[5] method published in literature.The average absolute deviations on the G2-1 test set for these models are 4.37,4.39,4.06 and 4.02 kJ· mol－ 1,respectively,compared with 4.27 for G3 and 4.05[32] for G3 //B3LYP on the same G2-1 test set.These results show further that the additivity or extrapolation approximation in the G3 theory is valid.However,the non-additive G3(QCI) procedures,which would be about four times of computer time consuming,in this work has been shown[10] more reliable in the energy calculation of species at non-equilibrium geometry.The maximum deviation of all of the four G3(QCI)′ s occurs on the electronic affinity of the oxygen atom,e.g.－ 16.7 for G3(QCI/fu1) and－ 16.9 kJ· mol－ 1 for others compared with 17.6 for G3 and 18.4 kJ· mol－ 1 for G3//B3LYP on the electronic affinity of NH radical.In addition,this work suggests that the G3large basis sets for the first-row atoms are too small or the level of core-electronic energy calculations for the anions are too low since most of the larger errors are in the respective electronic affinities and this need to be further studied.更多还原