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铁氧化物的第一性原理铁L边和氧K边X射线吸收近边结构(XANES)及X射线磁圆二色性(XMCD)光谱

First-Principles Fe L-Edge and O K-Edge XANES and XMCD Spectra for Iron Oxides.

作者信息

Sassi Michel, Pearce Carolyn I, Bagus Paul S, Arenholz Elke, Rosso Kevin M

机构信息

Pacific Northwest National Laboratory , Richland, Washington 99352, United States.

Department of Chemistry, University of North Texas , Denton, Texas 76203, United States.

出版信息

J Phys Chem A. 2017 Oct 12;121(40):7613-7618. doi: 10.1021/acs.jpca.7b08392. Epub 2017 Oct 2.

Abstract

X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectroscopies are tools in widespread use for providing detailed local atomic structure, oxidation state, and magnetic structure information for materials and organometallic complexes. The analysis of these spectra for transition-metal L-edges is routinely performed on the basis of ligand-field multiplet theory because one- and two-particle mean-field ab initio methods typically cannot describe the multiplet structure. Here we show that multireference configuration interaction (MRCI) calculations can satisfactorily reproduce measured XANES spectra for a range of complex iron oxide materials including hematite and magnetite. MRCI Fe L-edge XANES and XMCD spectra of Fe(II)O, Fe(III)O, and Fe(III)O in magnetite are found to be in very good qualitative agreement with experiment and multiplet calculations. Point-charge embedding and small distortions of the first-shell oxygen ligands have only small effects. Oxygen K-edge XANES/XMCD spectra for magnetite investigated by a real-space Green's function approach complete the very good qualitative agreement with experiment. Material-specific differences in local coordination and site symmetry are well reproduced, making the approach useful for assigning spectral features to specific oxidation states and coordination environments.

摘要

X射线吸收近边结构(XANES)和X射线磁圆二色性(XMCD)光谱是广泛使用的工具,用于提供材料和有机金属配合物的详细局部原子结构、氧化态和磁结构信息。由于单粒子和双粒子平均场从头算方法通常无法描述多重态结构,因此基于配体场多重态理论对过渡金属L边的这些光谱进行常规分析。在此,我们表明多参考组态相互作用(MRCI)计算能够令人满意地再现一系列复杂氧化铁材料(包括赤铁矿和磁铁矿)的实测XANES光谱。发现磁铁矿中Fe(II)O、Fe(III)O和Fe(III)O的MRCI Fe L边XANES和XMCD光谱与实验和多重态计算在定性上非常吻合。点电荷嵌入和第一壳层氧配体的小畸变只有很小的影响。通过实空间格林函数方法研究的磁铁矿的氧K边XANES/XMCD光谱与实验在定性上非常吻合。很好地再现了局部配位和位点对称性的材料特异性差异,使得该方法可用于将光谱特征归因于特定的氧化态和配位环境。

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