【摘要】 针对冻结芯电子近似 ,在 MP2/6-311G(d,p)级别上对 G2、 MP2/6-31G(d)和 MP2/6-311G(d,p)级别上对 G2(QCI)方法进一步考虑了芯电子相关能修正 ,尝试建立了 G2(fu2)、 G2(QCI/fu1)和 G2(QCI/fu2)方法 .G2-1 test set的反应能量计算结果表明 ,这些方法进一步减小了经验修正量； G2(QCI/fu1)和 G2(QCI/fu2)也比 G2(QCI)的总体精度有所提高；但 G2(fu2)在 G2基础上 ,总体精度没有改善 .G2(fu2)、 G2(QCI/fu1)和 G2(QCI/fu2)计算 G2-1 test set反应能量的平均绝对偏差分别为 5.11、 4.74和 4.81 kJ· mol－ 1,G2和 G2(QCI)分别为 5.09和 4.97 kJ· mol－ 1.更多还原

【Abstract】 In addition to our previous work of G2(fu1) in Ref.[8],we proposed a further core electronic correlation modification at MP2/6-31G(d) level to G2(QCI),namely G2(QCI/fu1),and that at MP2/6-311G(d,p) level to G2 and G2(QCI) theories,namely G2(fu2) and G2(QCI/fu2). The latter would need no additional calculation if the geometry is optimized at MP2(full)/6-311G(d,p) level. The modification energies,Δ E(fu1) andΔ E(fu2),were calculated via eq. Δ E(fu1)=E[MP2(full)/6-31G(d)]－ E[MP2(FC)/6-31G(d)] Δ E(fu2)=E[MP2(fu2)/6-311G(d,p)]－ E[MP2(FC)/6-311G(d,p)] G2 and G2(QCI) theories were modified via eq. E[G2(fu2)]=E(G2)＋ Δ E(fu2)－ HLC(G2)＋ HLC[G2(fu2)] E[G2(QCI/fu1)]=E[G2(QCI)]＋ Δ E(fu1)－ HLC[G2(QCI)]＋ HLC[G2(QCI/fu1)] E[G2(QCI/fu2)]=E[G2(QCI)]＋Δ E(fu2)－ HLC[G2(QCI)]＋ HLC[G2(QCI/fu2)] where, HLC[G2(fu2)]=－ 0.19nα－ 4.32nβ HLC[G2(QCI/fu1)]=－ 0.19nα－ 4.77 nβ HLC[G2(QCI/fu2)]=－ 0.19 nα－ 4.65 nβ It has been shown that the empirical High-Level-Correction (HLC) to either of the original G2 or G2(QCI) theory was reduced. G2(fu2) did not improve the over-all accuracy for the 125 G2-1 test set reaction energies,however both G2(QCI/fu1) and G2(QCI/fu2) did. The average absolute deviations (AAD) for the 125 reaction energies in the G2-1 test set were reduced from 4.97 for G2(QCI) to 4.74 for G2(QCI/fu1) and to 4.81 kJ· mol－ 1 for G2(QCI/fu2). The AAD was 5.11 for G2(fu2) compared with 5.09 kJ· mol－ 1 for G2. The reason for the larger AAD of G2(fu2) is probably due to that we did not use the better geometry of MP2(full)/6-311G(d,p) as presented in Ref. [11] ,and the 6-311G basis sets was somewhat unsatisfactory to describe both of the first- and second-row atoms as had been criticized in Ref.[9].更多还原