论文标题
中等强相关性方面的局部耦合群集方法的性能：Hückel-Möbius互连扩展的卟啉
Performance of Localized Coupled Cluster Methods in a Moderately Strong Correlation Regime: Hückel-Möbius Interconversions in Expanded Porphyrins
论文作者
论文摘要
局部轨道耦合簇理论最近已成为大型系统DFT的非经验替代方案。直觉上，人们可能会期望这种方法在高度离域的系统中的表现不佳。在目前的工作中，我们将其规范CCSD（t）和各种局部近似值应用于一组扩展的卟啉 - 可以在外部刺激下在Hückel，Figu-8和Möbius拓扑之间切换的系统。都考虑了最小值和异构化过渡状态。我们发现，Möbius（类似）结构的静态相关特性比其余结构更强，并且除非采用紧密的截止值，否则这会导致DLPNO-CCSD（T），甚至DLPNO-CCSD（T1）方法都会引起明显的误差。如果即使对于Möbius-type系统（或其他受强静态相关性困扰的系统），则需要对规范相对能量的次级/摩尔复制，则Nagy和Kallay和Kallay的LNO-CCSD（T）具有“紧密”设置可以提供的计算费用比PNO-LCCSD（tno-lccsd）更大的计算（T）（t）。与规范方法相比，更温和的CPU时间缩放。我们将目前的Polypyr21数据集作为局部轨道方法的基准，或更广泛地提出基准，以便低级方法处理具有静态相关性较大程度的能量学的能力。
Localized orbital coupled cluster theory has recently emerged as an nonempirical alternative to DFT for large systems. Intuitively, one might expect such methods to perform less well for highly delocalized systems. In the present work, we apply both canonical CCSD(T) and a variety of localized approximations thereto to a set of expanded porphyrins -- systems that can switch between Hückel, figure-eight, and Möbius topologies under external stimuli. Both minima and isomerization transition states are considered. We find that Möbius(-like) structures have much stronger static correlation character than the remaining structures, and that this causes significant errors in DLPNO-CCSD(T) and even DLPNO-CCSD(T1) approaches, unless TightPNO cutoffs are employed. If sub-kcal/mol reproduction of canonical relative energies is required even for Möbius-type systems (or other systems plagued by strong static correlation), then Nagy and Kallay's LNO-CCSD(T) method with "tight" settings can provide that, at much greater computational expense than either the PNO-LCCSD(T) or DLPNO-LCCSD(T) approaches but with still a much gentler CPU time scaling than canonical approaches. We would propose the present POLYPYR21 dataset as a benchmark for localized orbital methods, or more broadly, for the ability of lower-level methods to handle energetics with strongly varying degrees of static correlation.
