Consequences of realistic embedding for the L2,3 edge XAS of α-Fe2O3

Abstract

Cluster models of condensed systems are often used to simulate the core-level spectra obtained with X-ray Photoelectron Spectroscopy, XPS, or with X-ray Absorption Spectroscopy, XAS, especially for near edge features. The main objective of this paper is to examine the dependence of the predicted L_2,3 edge XAS of α-Fe₂O₃, an example of a high spin ionic crystal, on increasingly realistic models of the condensed system. It is shown that an FeO₆ cluster model possessing the appropriate local site symmetry describes most features of the XAS and is a major improvement over the isolated Fe³⁺ cation. In contrast, replacing next nearest neighbor positive point charges with Sc³⁺, a closed shell cation of similar spatial extent to Fe³⁺, only marginally improves the match to experiment. This work suggests that second nearest neighbor effects are negligible. Rather, major improvements to the predicted L_2,3 edge XAS likely requires additional many body effects that go beyond the present study in which the multiplets are restricted to arise from angular momentum coupling within a single open shell configuration.