Efficient and accurate treatment of weak pairs in local CCSD(T) calculations.
Efficient and accurate treatment of weak pairs in local CCSD(T) calculations.
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在本地 CCSD(T) 计算中高效、准确地处理弱对。
DOI：
10.1063/1.4826534
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
M. Schütz
中科院分区：
文献类型：
--
作者：
O. Masur;D. Usvyat;M. Schütz
局域耦合团簇理论基于（i）对占据的分子轨道对（或三重）列表的限制，以及（ii）将虚空间截断为轨道对（或三重）特定子空间。后者是由对能量的贡献相对于相关的局部占据轨道和虚轨道之间的距离的指数衰减引起的;前者仅由多项式R（-6）衰减相对于对的两个占据轨道之间的距离R。因此，对列表的限制更为关键，除非相应的轨道间距离很大，否则不应忽略对的贡献。在局域耦合团簇理论中，通常根据轨道间距离或对能量的二阶Møller-Plesset微扰理论（MP2）估计的大小来区分对。仅在全耦合集群级别处理强对，而仅在MP2级别处理弱对。然而MP2在某些情况下可能会有问题，例如，π堆积是不好的描述MP2等，我们建议取代MP2处理弱对的方法基于环CCD包括三阶图与R（-6）衰变行为。这种方法显然是优越的上级，它提供了更高的精度，而计算成本并不显着高于基于MP2的弱对的处理。
Local coupled cluster theory is based on (i) a restriction of the list of pairs (or triples) of occupied molecular orbitals, and (ii) a truncation of the virtual space to orbital pair (or triple) specific subspaces. The latter is motivated by an exponential decay of the contributions to the pair energy with respect to the distance between related local occupied and virtual orbitals; the former only by a polynomial R(-6) decay with respect to the distance R between the two occupied orbitals of the pair. Consequently, the restriction of the pair list is more critical, and contributions of pairs should not be neglected unless the corresponding interorbital distance is really large. In local coupled cluster theory pairs are usually discriminated on the basis of the interorbital distance, or the size of the 2nd order Møller-Plesset perturbation theory (MP2) estimate of the pair energy. Only strong pairs are treated at the full coupled cluster level, while weak pairs are treated just at the level of MP2. Yet MP2 might be problematic in certain cases, for example, π-stacking is badly described by MP2, etc. We propose to substitute the MP2 treatment of weak pairs by an approach based on ring-CCD by including third-order diagrams with R(-6) decay behavior. Such an approach is clearly superior; it provides higher accuracy, while the computational cost is not significantly higher than that of a MP2 based treatment of weak pairs.
影响因子：
4.4
作者：
Hansen, Andreas;Liakos, Dimitrios G.;Neese, Frank
通讯作者：
Neese, Frank