Department of Chemistry , The Johns Hopkins University , Baltimore , Maryland 21218 , United States.
J Chem Theory Comput. 2019 Sep 10;15(9):4945-4955. doi: 10.1021/acs.jctc.9b00568. Epub 2019 Aug 14.
A thorough study of the performance of delta-coupled-cluster (ΔCC) methods for calculations of core-ionization energies for elements of the first long row of the periodic table is reported. Inspired by the core-valence separation (CVS) scheme in response theories, a simple CVS scheme of excluding the vacant core orbital from the CC treatment has been adopted to solve the convergence problem of the CC equations for core-ionized states. Dynamic correlation effects have been shown to make important contributions to the computed core-ionization energies, especially to chemical shifts of these quantities. The maximum absolute error (MaxAE) and standard deviation (SD) of delta-Hartree-Fock results for chemical shifts of core-ionization energies with respect to the corresponding experimental values amount to more than 1.7 and 0.6 eV, respectively. In contrast, the inclusion of electron correlation in ΔCC singles and doubles augmented with a noniterative triples correction [ΔCCSD(T)] method significantly reduces the corresponding deviations to around 0.3 and 0.1 eV. With the consideration of basis set effects and the corrections to the CVS approximation, ΔCCSD(T) has been shown to provide highly accurate results for absolute values of core-ionization energies, with a MaxAE of 0.22 eV and SD of 0.13 eV. To further demonstrate the usefulness of ΔCCSD(T), calculations of carbon K-edge ionization energies of ethyl trifluoroacetate, a molecule of significant interest to the study of X-ray spectroscopy and dynamics, are reported.
本文全面研究了用于计算第一长周期元素的芯级电离能的Delta-耦合簇（ΔCC）方法的性能。受响应理论中芯价分离（CVS）方案的启发，采用了一种简单的 CVS 方案，即将空芯轨道从 CC 处理中排除，以解决 CC 方程对芯级电离态的收敛问题。动态相关效应对计算的芯级电离能有重要贡献，特别是对这些量的化学位移有重要贡献。Delta-Hartree-Fock 方法计算的芯级电离能的化学位移的最大绝对误差（MaxAE）和标准偏差（SD）与相应的实验值相比，分别超过 1.7 和 0.6 eV。相比之下，在 ΔCC 单激发和双激发中加入非迭代三激发校正[ΔCCSD（T）]方法，显著降低了相应的偏差，约为 0.3 和 0.1 eV。考虑到基组效应和 CVS 近似的校正，ΔCCSD（T）方法对芯级电离能的绝对值提供了高度准确的结果，其 MaxAE 为 0.22 eV，SD 为 0.13 eV。为了进一步证明 ΔCCSD（T）的有用性，报告了对三氟乙酸乙酯的碳 K 边电离能的计算，三氟乙酸乙酯是 X 射线光谱学和动力学研究中具有重要意义的分子。
