用W4理论、密度泛函方法、Gn方法和CBS方法对碳原子团簇Cn（n=2- 10）的原子化能进行了研究
Atomization energies of the carbon clusters Cn (n=2--10) revisited by means of W4 theory as well as density functional, Gn, and CBS methods
摘要：
本文用W_4理论和W_（3.2）理论重新研究了碳团簇C $_n$（n=2- 10）的热化学。特别是较大的集群表现出非常明显的后CCSD（T）相关效应。尽管如此，我们最好的计算总原子化能量同意令人惊讶的是，与1991年从缩放CCD（ST）/6- 31 G * 数据获得的估计。精确地再现C $_2$中的小的单重态-三重态分裂需要包括连接的五重态和六重态激发。C $_4$中的CCSD（T）后相关效应稳定了线性形式。在C $_6$，C $_8$，和C $_{10}$的线性/循环平衡没有强烈的影响，由连接的四元组，但他们受到影响的高阶三元组，有利于聚乙炔环，但不利于累积的。在CCSD（T）基组极限附近，C $_{10}$在阱底结构中确实经历键角交替，尽管预计在振动平均结构中不存在。这些系统的热化学，特别是较长的线性链，是密度泛函方法的一个特别困难的测试。特别是对于较小的链和环，双杂化泛函明显优于传统的DFT泛函。在化合物热化学方案中，G4明显优于G $n$家族的其他成员。我们对0 K时总原子化能的最佳估计值在1 kJ/mol至C $_5$范围内是可靠的，在1 kcal/mol至C $_9$范围内是可靠的。
英文摘要：
The thermochemistry of the carbon clusters C$_n$ (n=2--10) has been revisited by means of W4 theory and W3.2lite theory. Particularly the larger clusters exhibit very pronounced post-CCSD(T) correlation effects. Despite this, our best calculated total atomization energies agree surprisingly well with 1991 estimates obtained from scaled CCD(ST)/6-31G* data. Accurately reproducing the small singlet-triplet splitting in C$_2$ requires inclusion of connected quintuple and sextuple excitations. Post-CCSD(T) correlation effects in C$_4$ stabilize the linear form. Linear/cyclic equilibria in C$_6$, C$_8$, and C$_{10}$ are not strongly affected by connected quadruples, but they are affected by higher-order triples, which favor polyacetylenic rings but disfavor cumulenic ones. Near the CCSD(T) basis set limit, C$_{10}$ does undergo bond angle alternation in the bottom-of-the-well structure, although it is expected to be absent in the vibrationally averaged structure. The thermochemistry of these systems, and particularly the longer linear chains, is a particularly difficult test for density functional methods. Particularly for the smaller chains and the rings, double-hybrid functionals clearly outperform convential DFT functionals for these systems. Among compound thermochemistry schemes, G4 clearly outperforms the other members of the G$n$ family. Our best estimates for total atomization energies at 0 K should be reliable to 1 kJ/mol up to C$_5$ inclusive, and to better than 1 kcal/mol up to C$_9$ inclusive.
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