Development of local Coupled Cluster Linear Response method for the calculation of excited state properties of extended molecular systems

在过去的十年里，针对扩展的分子系统的新的从头计算方法已经被开发出来。这些方法的特点是计算成本与分子大小的比例相对较低。在处理电子关联的背景下，这是通过借助于局部关联方法利用动态关联效应的短期性质来实现的。局域关联方法，特别是结合密度拟合近似计算电子排斥积分，是目前在高关联水平(如耦合团簇(CC)理论)处理系统的一种有价值的工具，否则只能用不太精确的方法，如密度泛函理论。然而，目前这些方法仅限于电子基态(GS)中的“封闭壳”组态。本项目的目的是发展基于含时CC(响应)理论的电子激发态性质的局域关联方法。作为基本的CC模型，我们选择CC2，并且只对昂贵的双取代引入局部近似。

During the last decade novel ab initio methods targeting extended molecular systems have been developed. These methods are characterised by comparatively low scalings of the computational cost with molecular size. In the context of the treatment of electron correlation this was achieved by exploiting the short-range nature of dynamic correlation effects by virtue of Local Correlation methods. Local Correlation methods, especially in combination with the Density Fitting approximation for the evaluation of electron repulsion integrals, are nowadays a valuable tool to treat systems at highly correlated levels (e.g. Coupled Cluster (CC) theory), which otherwise would only be accessible by less accurate methods, such as Density Functional Theory. However, presently, these methods are restricted to ’closed shell’ configurations in the electronic Ground State (GS). The aim of the present project is the development of local correlation methods for properties of electronically excited states, based on time-dependent CC (response) theory. As the underlying CC model we choose CC2 and local approximations are introduced only for the costly doubles substitutions.