Journal of Electron Microscopy 51:S107-S112 (2002)
© 2002 Oxford University Press
Full-length paper |
First principles calculation of ELNES by LCAO methods
1Department of Materials Science and Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan,
2Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA and
3Department of Physics, University of Missouri-Kansas City, Kansas City, MO 64110-2499, USA
To whom correspondence should be addressed. E-mail: itanaka{at}MTL.kyoto-u.ac.jp
Our recent works to reproduce and interpret experimental electron energy-loss near-edge structures (ELNES) are reviewed. Wave functions are significantly localized at the final state of the excitation to make the ELNES. Inclusion of core-hole effects is, therefore, mandatory to calculate ELNES. The molecular orbital approach using small clusters can reproduce the spectral features qualitatively well, since wave functions are forced to be localized by the cluster method. The linear combination of atomic orbitals (LCAO)-based cluster method has the advantage of interpreting the origin of the spectral features in a simple manner, especially when combined with overlap population diagrams. Quantitative reproduction of ELNES at edges of normal sp-elements can be made by LCAO-based band-structure calculations when sufficiently large supercells are chosen and the dipole matrix elements are computed. Contrary to these ‘normal’ edges, the L2,3 edge of the 3d-transition metal elements cannot be reproduced in these ways, because the interactions between 2p-hole and 3d electrons as well as the spin-orbit coupling are not negligible. The need for relativistic many-electrons calculations is, therefore, emphasized.
Keywords core-hole effects, boron nitride, cluster method, supercell method, multi-electron calculations, relativistic theory