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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Assessment of density functionals for pi systems: Energy differences between cumulenes and poly-ynes; Proton affinities, bond length alternation, and torsional potentials of conjugated polyenes; and proton affinities of conjugated Shiff bases
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Assessment of density functionals for pi systems: Energy differences between cumulenes and poly-ynes; Proton affinities, bond length alternation, and torsional potentials of conjugated polyenes; and proton affinities of conjugated Shiff bases

机译：pi系统密度泛函的评估：枯烯和聚炔之间的能量差;质子亲和力，键长交替和共轭多烯的扭转势; Shiff基的质子和质子亲和力

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Woodcock et al. [J. Phys. Chem. A 2002, 106, 11923] pointed out that no density functional was able to obtain the correct sign of the relative energies of the allene and propyne isomers of C3H4 and that density functional theory (DFT) predicts that poly-ynes are insufficiently stabilized over cumulenes for higher homologues. In the present work, we show that the recent M05 density functional predicts the correct ordering of allene and propyne and gives a mean unsigned error (MUE) of only 1.8 kcal/mol for the relative energies of the two isomers of C3H4, C5H4, and C7H4. Two other recent functionals, M05-2X and PWB6K, also give reasonably low MUEs, 2.7 and 3.0 kcal/mol, respectively, as compared to 6.2 kcal/ mol for the popular B3LYP functional. Another challenging problem for density functionals has been a tendency to overpolarize conjugated pi systems. We test this here by considering proton affinities of conjugated polyenes and conjugated Schiff bases. Again M05-2X performs quite well, with MUEs of 2.1 and 3.9 kcal/ mol, respectively, as compared to 5.8 and 5.9 kcal/ mol for B3LYP. Averaged over the three problems, M05-2X has a MUE of 3.0 kcal/ mol, the BMK functional of Boese et al. has an MUE of 3.2 kcal/ mol, and M05 has an MUE of 5.1 kcal/ mol. Twenty-two other tested functionals have MUEs of 5.2-8.1 kcal/ mol averaged over the three test problems. Both M05 and M05-2X do quite well, compared to other density functionals, for torsion potentials in butadiene and styrene, and M05 does very well for bond length alternation in conjugated polyenes. Since the M05 functional has broad accuracy for main group and transition metal chemistry and M05-2X has broad accuracy for main group chemistry, we conclude that significant progress is being made in improving the performance of DFT across a wide range of problem types.
机译：Woodcock等。 [J.物理化学[2002，106，11923]指出没有密度泛函能够获得C3H4的丙二烯和丙炔异构体的相对能的正确符号，并且密度泛函理论（DFT）预测聚-炔在异丙苯上的稳定性不足。对于更高的同系物。在目前的工作中，我们表明最近的M05密度泛函预测了丙二烯和丙炔的正确顺序，并且给出了C3H4，C5H4和C3H4两个异构体的相对能量的平均无符号误差（MUE）仅1.8 kcal / mol。 C7H4。与最近流行的B3LYP官能团的6.2 kcal / mol相比，其他两种最近的官能团M05-2X和PWB6K的MUE也分别较低，分别为2.7和3.0 kcal / mol。密度泛函的另一个挑战性问题是共轭pi系统过极化的趋势。我们在这里通过考虑共轭多烯和共轭席夫碱的质子亲和力进行测试。同样，M05-2X的性能相当好，其MUE分别为2.1和3.9 kcal / mol，而B3LYP的MUE分别为5.8和5.9 kcal / mol。对这三个问题取平均值，M05-2X的MUE为3.0 kcal / mol，是Boese等人的BMK功能。 MUE的MUE为3.2 kcal / mol，M05的MUE为5.1 kcal / mol。在这三个测试问题上，其他二十二个测试功能的MUE平均为5.2-8.1 kcal / mol。与其他密度官能团相比，M05和M05-2X在丁二烯和苯乙烯中的扭转潜力方面都表现出色，而M05在共轭多烯中的键长变化方面则表现出色。由于M05官能团对主族和过渡金属化学具有广泛的准确性，而M05-2X对主族化学具有广泛的准确性，因此我们得出结论，在改善各种问题类型的DFT性能方面，正在取得重大进展。

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