Quantifying the Application of FEFF to f-derived Spectral Structure
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.280
QUANTIFYING THE APPLICATION OF FEFF TO F-DERIVED SPECTRAL STRUCTURE J. G. Tobin,1,* and D. Sokaras2,# 1
University of Wisconsin-Oshkosh, Oshkosh, WI, USA 54901, USA
2
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
*Email: [email protected], #Email: [email protected]
ABSTRACT
Applying the Green's function based code FEFF to 5f derived features in actinide materials is potentially a very rewarding endeavor. However, there are some limitations that must be addressed. As part of the effort to quantify this process, FEFF has been applied to a few simplified 4f systems. The preliminary results of this investigation are discussed below.
INTRODUCTION: FEFF is a Green’s Function spectral simulation program used in xray absorption spectroscopy and related techniques, including self-consistent real space multiple-scattering code for simultaneous calculations of x-ray-absorption spectra and electronic structure, particularly for Extended X-ray Absorption Fine Structure (EXAFS). [1 - 5] In general, FEFF has proven itself to be a powerful data analysis tool, but with some limitations when applied to 5f related transitions. [5 - 9] To test the behavior of FEFF in connection with f derived features, simplified rare earth constructs have been utilized. Here, rare earth atoms have been placed in the center of an fcc Cu cluster, as
1
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shown in the inset in Figure 1. The idea behind this is to reduce the interactions between the central and surrounding atoms, isolating less perturbed 4f behavior.
Figure 1
The 4f contributions to the Ce M 5 (orange line), M4 (purple line), N5 (orange +) and N4
(purple +) XES, as well as the occupied (E < 0) f (red) and p (green dash) DOS. Inset, topmost part of figure: a schematic showing part of the 78 Cu atom fcc matrix (tan) surrounding the central atom (light red). For this figure, the central atom was Ce.
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RESULTS AND DISCUSSION: Shown in Figures 1 and 2 are the M4,5 and N4,5 4f X-ray Emission Spectroscopy (Figure 1) and the L-specific Density of States (LDOS, Figures 1 and 2). It is quite clear that the FEFF XES correlates with the occupied 4f and 6p DOS near the Fermi Energy. These are the states with transitions into the 3d and 4d holes allowed by electric dipole selection rules. [8, 9] The lifetime broadening here is too small: experimental results show much greater broadening. [10] However, the reduced lifetime broadening does have the advantage of providing a strong test of the XES-LDOS correlation.
Figure 2
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