I find the expression:(adsbygoogle = window.adsbygoogle || []).push({});

"In general, one can expand the atomic displacements in terms of all the lattice wave

modes (resembles a Fourier series expansion)"

at:

https://courses.cit.cornell.edu/ece407/Lectures/handout17.pdf

But I have not found the expression in any other literature. (In fact, some literature, like P.Y. Yu and M. Cardona: Fundamentals of Semiconductors, a long wavelength limitation seems to have been imposed.) Is the above-cited expression correct (in 3D lattice)?

Thank for your assistance.

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# Expanding atomic displacements in terms of all lattice wave modes?

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