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

在过去的十年中，新的针对扩展分子系统的从头算方法得到了发展。这些方法的特点是计算成本与分子大小的比例相对较低。在处理电子相关的情况下，这是通过利用局部相关方法利用动态相关效应的短程性质来实现的。局部相关方法，特别是结合密度拟合近似来评估电子排斥积分，现在是一个有价值的工具，用于处理高度相关水平的系统（例如耦合簇（CC）理论），否则只能通过密度泛函理论等不太准确的方法获得。然而，目前，这些方法仅限于电子基态（GS）中的“闭壳”构型。本项目的目的是基于时变CC（响应）理论，发展电子激发态性质的局部相关方法。作为底层CC模型，我们选择CC2，局部近似只用于代价高昂的双元替换。

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.