Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
J Chem Phys. 2023 Mar 7;158(9):094111. doi: 10.1063/5.0134459.
Methods for computing core-level ionization energies using self-consistent field (SCF) calculations are evaluated and benchmarked. These include a "full core hole" (or "ΔSCF") approach that fully accounts for orbital relaxation upon ionization, but also methods based on Slater's transition concept in which the binding energy is estimated from an orbital energy level that is obtained from a fractional-occupancy SCF calculation. A generalization that uses two different fractional-occupancy SCF calculations is also considered. The best of the Slater-type methods afford mean errors of 0.3-0.4 eV with respect to experiment for a dataset of K-shell ionization energies, a level of accuracy that is competitive with more expensive many-body techniques. An empirical shifting procedure with one adjustable parameter reduces the average error below 0.2 eV. This shifted Slater transition method is a simple and practical way to compute core-level binding energies using only initial-state Kohn-Sham eigenvalues. It requires no more computational effort than ΔSCF and may be especially useful for simulating transient x-ray experiments where core-level spectroscopy is used to probe an excited electronic state, for which the ΔSCF approach requires a tedious state-by-state calculation of the spectrum. As an example, we use Slater-type methods to model x-ray emission spectroscopy.
使用自洽场 (SCF) 计算来计算芯能级电离能的方法进行了评估和基准测试。这些方法包括一种“完全芯空穴”（或“ΔSCF”）方法，该方法充分考虑了电离时轨道弛豫，但也包括基于 Slater 跃迁概念的方法，其中结合能是从分数占据 SCF 计算得到的轨道能级估算的。还考虑了一种使用两个不同分数占据 SCF 计算的推广方法。对于一组 K 壳层电离能数据集，最好的 Slater 型方法相对于实验的平均误差为 0.3-0.4 eV，其精度与更昂贵的多体技术相当。具有一个可调参数的经验转移过程将平均误差降低到 0.2 eV 以下。这种移位 Slater 跃迁方法是一种使用仅初始态 Kohn-Sham 本征值计算芯能级结合能的简单实用方法。它不需要比 ΔSCF 更多的计算工作量，并且可能特别适用于模拟瞬态 X 射线实验，其中芯层光谱学用于探测激发的电子态，对于该态，ΔSCF 方法需要对谱进行繁琐的逐态计算。作为一个例子，我们使用 Slater 型方法来模拟 X 射线发射光谱。
