A rigorous study is presented of the physical processes related to X-Ray photoelectron spectroscopy, XPS, in the 4f level of U oxides, which, as well as being of physical interest in themselves, are representative of XPS in heavy metal oxides. In particular, we present compelling evidence for a new view of the screening of core-holes that extends prior understandings. Our analysis of the screening focuses on the covalent mixing of high lying U and O orbitals as opposed to the, more common, use of orbitals that are nominally pure U or pure O. It is shown that this covalent mixing is quite different for the initial and final, core-hole, configurations and that this difference is directly related to the XPS satellite intensity. Furthermore, we show that the high-lying U d orbitals as well as the U(5f) orbital may both contribute to the core-hole screening, in contrast with previous work that has only considered screening through the U(5f) shell. The role of modifying the U-O interaction by changing the U-O distance has been investigated and an unexpected correlation between U-O distance and XPS satellite intensity has been discovered. The role of flourite and octahedral crystal structures for U(IV) oxides has been examined and relationships established between XPS features and the covalent interactions in the different structures. The physical views of XPS satellites as arising from shake processes or as arising from ligand to metal charge transfers are contrasted; our analysis provides strong support that shake processes give a more fundamental physical understanding than charge transfer. Our theoretical studies are based on rigorous, strictly ab initio determinations of the electronic structure of embedded cluster models of U oxides with formal U(VI) and U(IV) oxidation states. Our results provide a foundation that makes it possible to establish quantitative relationships between features of the XPS spectra and materials properties.

中文翻译：

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U（VI）和U（IV）氧化物的铀4f XPS的理论模型。

对X射线光电子能谱XPS的4f级U氧化物的物理过程进行了严格的研究，它本身也具有物理意义，是重金属氧化物中XPS的代表。尤其是，我们提供了令人信服的证据，证明了对孔洞筛查的新观点可以扩展先前的理解。我们对筛选的分析着眼于高位U和O轨道的共价混合，而不是通常使用名义上纯U或纯O的轨道的共价混合。研究表明，这种共价混合在初始时是完全不同的以及最终的核心孔配置，并且这种差异与XPS卫星强度直接相关。此外，我们表明，与以前只考虑通过U（5f）壳进行筛选的工作相比，高空的U d轨道以及U（5f）轨道都可能对芯孔筛选有所贡献。已经研究了通过改变UO距离来修改UO相互作用的作用，并发现了UO距离与XPS卫星强度之间的意外关联。已经检查了U（IV）氧化物的萤石和八面体晶体结构的作用，并确定了XPS功能与不同结构中的共价相互作用之间的关系。对比了XPS卫星由于震荡过程或由于配体向金属的电荷转移而产生的物理观点；我们的分析为震动过程提供了比电荷转移更基本的物理理解的有力支持。我们的理论研究基于对具有正式U（VI）和U（IV）氧化态的U氧化物的嵌入式簇模型的电子结构的严格，从头开始的确定。我们的结果为建立XPS光谱特征与材料特性之间的定量关系提供了基础。