Simons Megan, Matthews Devin A
Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States.
J Chem Theory Comput. 2022 Jun 14;18(6):3759-3765. doi: 10.1021/acs.jctc.2c00268. Epub 2022 May 10.
The phenomenon of orbital relaxation upon excitation of core electrons is a major problem in the linear-response treatment of core-hole spectroscopies. Rather than addressing relaxation through direct dynamical correlation of the excited state via equation-of-motion coupled cluster theory (EOMEE-CC), we extend the alternative similarity-transformed equation-of-motion coupled cluster theory (STEOMEE-CC) by including the core-valence separation (CVS) and correlation of triple excitations only within the calculation of core ionization energies. This new method, CVS-STEOMEE-CCSD+cT, significantly improves on CVS-EOMEE-CCSD and unmodified CVS-STEOMEE-CCSD when compared to full CVS-EOM-CCSDT for K-edge core-excitation energies of a set of small molecules. The improvement in both absolute and relative (shifted) peak positions is nearly as good as that for transition-potential coupled cluster (TP-CC), which includes an explicit treatment of orbital relaxation, and CVS-EOMEE-CCSD*, which includes a perturbative treatment of triple excitations.
在芯电子激发时发生的轨道弛豫现象是芯孔光谱线性响应处理中的一个主要问题。我们没有通过运动方程耦合簇理论（EOMEE-CC）对激发态进行直接动力学关联来处理弛豫，而是扩展了替代的相似变换运动方程耦合簇理论（STEOMEE-CC），仅在芯电离能的计算中纳入芯价分离（CVS）和三重激发的关联。与用于一组小分子K边芯激发能的全CVS-EOM-CCSDT相比，这种新方法CVS-STEOMEE-CCSD+cT在CVS-EOMEE-CCSD和未修正的CVS-STEOMEE-CCSD基础上有显著改进。在绝对和相对（位移）峰位置上的改进几乎与过渡势耦合簇（TP-CC，其中明确处理了轨道弛豫）以及CVS-EOMEE-CCSD*（其中对三重激发进行了微扰处理）一样好。
