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Band structure (BS) methods used in EELS modeling are applied in reciprocal space based on density functional theory (DFT) [1  2]. 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 [3].
Among the various codes available for DFT calculations, two codes are commercially available and can be used to model ELNES: i) Pseudopotential code CASTEP, which was developed in University of Cambridge [4  5] (www.accelrys.com/cerius2/castep.html) and ii) WIEN2k which was developed at the Vienna University of Technology [6  7] (www.wien2k.at.).
[1] Hohenberg, P., Kohn, W., 1964. Inhomogeneous electron gas. Phys. Rev. 136 (3B), B864–B871.
[2] Kohn, W., Sham, L.J., 1965. Selfconsistent equations including exchange and correlation effects. Phys. Rev. 140 (4A), A1133–A1138.
[3] 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.
[4] Payne, M.C., Teter, M.P., Allan, D.C., Arias, T.A., Joannopoulos, J.D., 1992. Iterative minimization techniques for ab initio totalenergy calculations: molecular dynamics and conjugate gradients. Rev. Mod. Phys. 64 (4), 1045  1097.
[5] Pickard, C.J., Payne, M.C., 1997. Ab initio EELS: beyond the fingerprint. In: Electron Microscopy and Analysis Group Conference EMAG97. IOP Publishing Ltd, pp. 179–182.
[6] Blaha, P., Schwarz, K., Sorantin, P., 1990. Fullpotential, linearized augmented plane wave programs for crystalline systems. Comput. Phys. Commun. 59, 399–415.
[7] HébertSouche, C., Louf, P.H., Blaha, P., Nelhiebel, M., Luitz, J., Schattschneider, P., Schwarz, K., Jouffrey, B., 2000. The orientation dependent simulation of ELNES. Ultramicroscopy 83 (1–2), 9–16.
