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首页> 外文期刊>The Journal of Chemical Physics >A COMPLETE BASIS SET MODEL CHEMISTRY .5. EXTENSIONS TO SIX OR MORE HEAVY ATOMS
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A COMPLETE BASIS SET MODEL CHEMISTRY .5. EXTENSIONS TO SIX OR MORE HEAVY ATOMS

机译：完整的基础设定模型化学.5。扩展到六个或更多个重原子

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The major source of error in most ab initio calculations of molecular energies is the truncation of the one-electron basis set. Extrapolation to the complete basis set second-order (CBS2) limit using the N-1 asymptotic convergence of N-configuration pair natural orbital (PNO) expansions can be combined with the use of relatively small basis sets for the higher-order (i.e., MP3, MP4, and QCI) correlation energy to develop cost effective computational models. Following this strategy, three new computational models denoted CBS-4, CBS-q, and CBS-Q, are introduced. The mean absolute deviations (MAD) from experiment for the 125 energies of the G2 test set are 2.0, 1.7, and 1.0 kcal/mol, respectively. These results compare favorably with the MAD for the more costly G2(MP2), G2, and CBS-QCI/APNO models (1.6, 1.2, and 0.5 kcal/mol, respectively). The error distributions over the G2 test set are indistinguishable from Gaussian distribution functions for all six models, indicating that the rms errors can be interpreted in the same way that experimental uncertainties are used to assess reliability. However, a broader range of examples reveals special difficulties presented by spin contamination, high molecular symmetry, and localization problems in molecules with multiple lone pairs on the same atom. These characteristics can occasionally result in errors several times the size expected from the Gaussian distributions. Each of the CBS models has a range of molecular size for which it is the most accurate computational model currently available. The largest calculations reported for these models include: The CBS-4 heat of formation of tetranitrohydrazine (91.5 +/- 5 kcal/mol), the CBS-4 and CBS-q isomerization energies for the ;conversion of azulene to naphthalene (Delta H-calc = -35.2 +/- 1.0 kcal/mol, Delta H-exp = -35.3 +/- 2.2 kcal/mol), and the CBS-Q heat of formation of SF6 (Delta H-calc = -286.6 +/- 1.3 kcal/mol, Delta H-exp = -288.3 +/- 0.2 kcal/mol). The CBS-Q value for the dissociation energy of a C-H bond in benzene (113.1 +/- 1.3 kcal/mol) is also in agreement with the most recent experimental result (112.0 +/- 0.6 kcal/mol). The CBS-QCI/APNO model is applicable to the prediction of the C-H bond dissociation energies for the primary (100.7 +/- 0.7 kcal/mol calc.) and secondary (97.7 +/- 0.7 kcal/mol calc., 97.1 +/- 0.4 kcal/mol exp.) hydrogens of propane. (C) 1996 American Institute of Physics. [References: 76]
机译：在大多数从头算分子能量的计算中，主要的误差来源是单电子基集的截断。使用N配置对自然轨道（PNO）展开的N-1渐近收敛性外推到完整的基集二阶（CBS2）极限可以与较高阶的相对较小基集的使用相结合（即， MP3，MP4和QCI）相关能量以开发具有成本效益的计算模型。按照这种策略，引入了三个新的计算模型，分别表示为CBS-4，CBS-q和CBS-Q。 G2测试设备的125个能量与实验的平均绝对偏差（MAD）分别为2.0、1.7和1.0 kcal / mol。对于成本更高的G2（MP2），G2和CBS-QCI / APNO模型（分别为1.6、1.2和0.5 kcal / mol），这些结果与MAD相比具有优势。对于所有六个模型，G2测试集上的误差分布与高斯分布函数没有区别，这表明均方根误差可以用与使用实验不确定性评估可靠性相同的方式来解释。但是，更多示例揭示了自旋污染，高分子对称性以及在同一原子上具有多个孤对的分子中的局部化问题所带来的特殊困难。这些特性有时会导致误差，其误差是高斯分布的预期大小的几倍。每个CBS模型都有一个分子大小范围，这是目前可用的最精确的计算模型。针对这些模型报道的最大计算包括：四硝基肼的CBS-4形成热（91.5 +/- 5 kcal / mol），Caz-4和CBS-q异构化能量;用于将a烯转化为萘（δH -calc = -35.2 +/- 1.0 kcal / mol，ΔH-exp = -35.3 +/- 2.2 kcal / mol）和SF6的CBS-Q形成热（ΔH-calc = -286.6 +/- 1.3 kcal / mol，ΔH-exp = -288.3 +/- 0.2 kcal / mol）。苯中C-H键的离解能的CBS-Q值（113.1 +/- 1.3 kcal / mol）也与最新的实验结果（112.0 +/- 0.6 kcal / mol）一致。 CBS-QCI / APNO模型适用于一次（100.7 +/- 0.7 kcal / mol的计算值）和二次（97.7 +/- 0.7 kcal / mol的计算值，97.1 +/-）的CH键解离能的预测-丙烷的氢为0.4 kcal / mol。 （C）1996年美国物理研究所。 [参考：76]

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