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Even though the electronic structure information is available in the low-loss EEL spectrum (see page4360), the interpretation is difficult because there is no direct relationship between the EELS and the density of states (DOS). Therefore, in contrast to ELNES, low-loss EELS has been much less widely used to measure and understand electronic structure. Low-loss EEL spectra have been calculated using density-functional theory (DFT) based on WIEN2k codes. [1, 2]
The WIEN2k code has recently been used for the calculation of electron energy loss spectra. [3] Low loss spectra are calculated with the OPTIC package while core loss spectra are calculated with the TELNES program.
Band structure (BS) methods used in EELS modeling are applied in reciprocal space based on density functional theory (DFT) [4 - 5]. BS methods were originally developed to derive the electron density. The advantage of BS methods is that based on ELNES and low loss spectra, many physical properties can be derived from the same calculation. Those properties can be band structure diagrams, density of states, elastic constants, optical properties, electron densities, etc. The drawback of BS methods is that they yield only ground states properties, and thus the calculation of excited states properties is not guaranteed to work. However, the calculation of ELNES and of low loss spectra with DFT works very well [6].
However, at very low energy losses, especially in the range of 0 to 5 eV, the current deconvolution methods for multiple inelastic scattering are not sufficiently accurate [7]. For instance, in this energy range, any differences between the experimental and modelled zero-loss peaks (ZLPs) can create large, random data spikes in the deconvoluted spectrum.
[1] V. J. Keast, Ab initio calculations of plasmons and interband transitions in the low-loss electron energy-loss spectrum, Journal of Electron Spectroscopy and Related Phenomena 143 (2005) 97–104.
[2] K. Schwarz, P. Blaha, G.K.H. Madsen, Comput. Phys. Commun. 147 (2002) 71.
[3] C. Hébert, Practical aspects of running the WIEN2k code for electron spectroscopy, Micron 38 (2007) 12–28.
[4] Hohenberg, P., Kohn, W., 1964. Inhomogeneous electron gas. Phys. Rev. 136 (3B), B864–B871.
[5] Kohn, W., Sham, L.J., 1965. Self-consistent equations including exchange and correlation effects. Phys. Rev. 140 (4A), A1133–A1138.
[6] Rez, P., Bruley, J., Brohan, P., Payne, M., Garvie, L.A.J., 1995. Review of
methods for calculating near edge structure. Ultramicroscopy 59, 159–167.
[7] U. Bangert and R. Barnes. Electron energy loss spectroscopy of defects in diamond. Phys. Stat. Sol. (A), 204 (7): 2201–2210, 2007.
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