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Approximate Methods for Taking Absorption into Account in the Dynamical Theory of Electron Diffraction
Author(s) -
Andrew J. W.,
Sheinin S. S.
Publication year - 1976
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220730207
Subject(s) - degenerate energy levels , perturbation theory (quantum mechanics) , bloch wave , diffraction , basis (linear algebra) , electron , statistical physics , mixing (physics) , mathematics , theoretical physics , physics , quantum mechanics , geometry
Approximate methods for taking absorption into account in the dynamical theory of electron diffraction can be obtained from the exact theory by assuming that mixing between certain pairs of Bloch waves is unimportant and can therefore be neglected. The assumptions required to reduce the exact theory to the lower order perturbation theories previously published in the literature are examined. This is of interest since an understanding of these assumptions provides a physical basis for comparing these theories as well as giving the insight required to develop new approximations. The details of a new approximate theory, referred to as the sub‐matrix method, are also given. This approach has a number of advantages over other approximate methods. Firstly, it is applicable under conditions which lead to either non‐degenerate, quasi‐degenerate or degenerate Bloch waves. As well the method can give very close agreement with the exact theory while at the same time providing advantages from a computational point of view.