DTU Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, UiTThe Arctic University of Norway, 9037 Tromsø, Norway.
J Phys Chem A. 2023 Feb 23;127(7):1775-1793. doi: 10.1021/acs.jpca.2c08181. Epub 2023 Feb 10.
We present an implementation of a damped response framework for calculating resonant inelastic X-ray scattering (RIXS) at the equation-of-motion coupled-cluster singles and doubles (CCSD) and second-order approximate coupled-cluster singles and doubles (CC2) levels of theory in the open-source program . This framework lays the foundation for future extension to higher excitation methods (notably, the coupled-cluster singles and doubles with perturbative triples, CC3) and to multilevel approaches. Our implementation adopts a fully relaxed ground state and different variants of the core-valence separation projection technique to address convergence issues. Illustrative results are compared with those obtained within the frozen-core core-valence separated approach, available in Q-Chem, as well as with experiment. The performance of the CC2 method is evaluated in comparison with that of CCSD. It is found that, while the CC2 method is noticeably inferior to CCSD for X-ray absorption spectra, the quality of the CC2 RIXS spectra is often comparable to that of the CCSD level of theory, when the same valence excited states are probed. Finally, we present preliminary RIXS results for a solvated molecule in aqueous solution.
我们提出了一个阻尼响应框架的实现，用于在运动方程耦合簇单和双（CCSD）和二阶近似耦合簇单和双（CC2）理论水平上计算共振非弹性 X 射线散射（RIXS），该框架为未来扩展到更高激发方法（特别是耦合簇单和双与微扰三重态，CC3）和多级方法奠定了基础。我们的实现采用完全松弛的基态和不同的核壳分离投影技术变体来解决收敛问题。说明性结果与 Q-Chem 中可用的冻结核壳分离方法以及实验结果进行了比较。我们还评估了 CC2 方法与 CCSD 方法的性能。结果发现，虽然 CC2 方法在 X 射线吸收光谱方面明显不如 CCSD，但当探测相同价激发态时，CC2 RIXS 光谱的质量通常与 CCSD 理论水平相当。最后，我们给出了水溶液中溶剂化分子的初步 RIXS 结果。
