Thank you stefano for answering my questions. Now I have a question about the crossing of the phonon branches. I know there are some rules govening the phonon branch crossing such as branches belonging to the same irrep will not cross each other. I don't know how PHONON manages this problem. I have never seen any crossing(in the sense of my understanding) of the dispersion curves calculated by PHONON, only tangent touching. But some of the experimental results did indicate crossing of the curves. Could anyone give some comments on this? Thanks!
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