运动方程MLCCSD和CCSD-in-HF振子强度及其在核激发中的应用
Equation-of-motion MLCCSD and CCSD-in-HF oscillator strengths and their application to core excitations
摘要：
本文提出了一种基于运动方程振子强度的多层CCSD（MLCCSD）模型的实现方法，其中CCS被用作低层方法（CCS/CCSD）。在这个模型中，团簇算符的双激发被限制在活动轨道空间，而单激发是不受限制的。计算氮K-边光谱的腺苷，腺苷三磷酸（ATP），和ATP-水系统被用来证明该模型的性能。投影原子轨道（PAO）用于将虚拟空间划分为活动和非活动轨道集。利用Hartree-Fock密度的Cholesky分解来划分占据轨道。这种Cholesky-PAO划分是廉价的，缩放为$\mathcal{O}(N^3)$，并且适合于计算在特征上局部化的核心激发。通过将团簇算符的单激发限制在活性空间，以及双激发，得到了CCSD-in-HF模型。比较了MLCCSD和CCSD-in-HF两种模型对腺苷和ATP体系的核心激发光谱的计算结果。
英文摘要：
We present an implementation of equation-of-motion oscillator strengths for the multilevel CCSD (MLCCSD) model where CCS is used as the lower level method (CCS/CCSD). In this model, the double excitations of the cluster operator are restricted to an active orbital space, whereas the single excitations are unrestricted. Calculated nitrogen K-edge spectra of adenosine, adenosine triphosphate (ATP), and an ATP-water system are used to demonstrate the performance of the model. Projected atomic orbitals (PAOs) are used to partition the virtual space into active and inactive orbital sets. Cholesky decomposition of the Hartree-Fock density is used to partition the occupied orbitals. This Cholesky-PAO partitioning is cheap, scaling as $\mathcal{O}(N^3)$, and is suitable for the calculation of core excitations which are localized in character. By restricting the single excitations of the cluster operator to the active space, as well as the double excitations, the CCSD-in-HF model is obtained. A comparison of the two models---MLCCSD and CCSD-in-HF---is presented for the core excitation spectra of the adenosine and ATP systems.
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