Kohn Anomaly and Avoided Crossing (Anticrossing/Level Repulsion) are terms that are found to be used when discussing phonon dispersion. The former (see last paragraph, page 198) is related to electron-phonon coupling, while the latter (refer 2nd paragraph, page 55) is related to phonon-phonon coupling. Both phenomena lower the phonon frequency.
Are these concepts same, related or different?
