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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Ab Initio Studies of π···π Interactions: The Effects of Quadruple Excitations
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Ab Initio Studies of π···π Interactions: The Effects of Quadruple Excitations

机译：π···π相互作用的从头算研究：四重激发的影响

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摘要

To examine the effects of including quadruple excitations in the electron correlation treatment when computing the binding energy of van der Waals dimers, we have calculated MP2, CCSD, CCSD(T), and CCSD(TQ) interaction energies for several van der Waals complexes ranging from helium dimer to furan dimer. Through comparison of CCSD(TQ) and CCSD(T) binding energies the first direct assessment of the effects of quadruple excitations on π···π interactions is presented. The influence of triple excitations is assessed not only in the conventional manner that permeates the literature (comparison of CCSD(T) and MP2 interaction energies) but also via comparison of CCSD(T) and CCSD data. In systems exhibiting significant electron delocalization, it is well-known that triples contributions to binding energy are quite large (on the order of 1 kcal mol~(-1)). In these cases, quadruple excitations are nonnegligible and tend to be an order of magnitude smaller than the correction to the binding energy from triple excitations (on the order of 0.1 kcal mol~(-1)). The largest quadruples correction observed was +0.2 kcal mol~(-1) for the furan dimer.
机译：在计算范德华二聚体的结合能时，要检查在电子相关处理中包括四重激发的影响，我们计算了范德华配合物的MP2，CCSD，CCSD（T）和CCSD（TQ）相互作用能从氦二聚体到呋喃二聚体通过比较CCSD（TQ）和CCSD（T）结合能，首次直接评估了四重激发对π···π相互作用的影响。三重激发的影响不仅可以通过渗透文献的常规方式（CCSD（T）和MP2相互作用能的比较）来评估，还可以通过比较CCSD（T）和CCSD数据来评估。在表现出显着电子离域的系统中，众所周知，对结合能的三重贡献非常大（约为1 kcal mol〜（-1））。在这些情况下，四重激发是不可忽略的，并且往往比三重激发对结合能的校正小一个数量级（约0.1 kcal mol〜（-1））。呋喃二聚体的最大四倍校正为+0.2 kcal mol〜（-1）。

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