Bagus Paul S, Sousa Carmen, Illas Francesc
Department of Chemistry, University of North Texas, Denton, TX 76203-5017, USA.
Phys Chem Chem Phys. 2020 Oct 15;22(39):22617-22626. doi: 10.1039/d0cp03569f.
The equivalent core model, or the Z + 1 approximation, has been used to interpret the binding energy, BE, shifts observed in X-ray photoelectron spectroscopy, XPS; in particular to relate these shifts to their origin in the electronic structure of the system. Indeed, a recent paper has claimed that the equivalent core model provides an intuitive chemical view of XPS BE shifts. In the present paper, we present a detailed comparison of the electronic structure provided from rigorous core-hole theory and from the equivalent core model to assess the validity and the utility of the use of the equivalent core model. This comparison shows that the equivalent core model provides a qualitative view of the different properties of initial and core-hole electronic structure. It is also shown that a very serious limitation of the equivalent core model is that it fails to distinguish between initial and final state contributions to the shifts of BEs which seriously reduces the utility of the information obtained with the equivalent core model. Indeed, there is a danger of making an incorrect assignment of the importance of relaxation because the equivalent core model appears to stress the role of final state effects. Given the importance of the distinction of initial and final state effects, we provide rigorous definitions of these two effects and we discuss an example where an incorrect interpretation was made based on the use of the equivalent core model.
等效芯模型，即Z + 1近似，已被用于解释X射线光电子能谱（XPS）中观察到的结合能（BE）位移；特别是将这些位移与其在系统电子结构中的起源联系起来。事实上，最近有一篇论文声称等效芯模型提供了XPS结合能位移的直观化学观点。在本文中，我们对严格的芯孔理论和等效芯模型所提供的电子结构进行了详细比较，以评估等效芯模型使用的有效性和实用性。这种比较表明，等效芯模型提供了初始和芯孔电子结构不同性质的定性观点。还表明等效芯模型的一个非常严重的局限性在于它无法区分对结合能位移的初始态和终态贡献，这严重降低了用等效芯模型获得的信息的实用性。实际上，存在对弛豫重要性进行错误归因的风险，因为等效芯模型似乎强调了终态效应的作用。鉴于区分初始态和终态效应的重要性，我们给出了这两种效应的严格定义，并讨论了一个基于等效芯模型使用而做出错误解释的例子。
