<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Imaginary frequencies are usually a sign of a mechanical instability, as discussed many times in this forum as well as in many condensed-matter textbooks. I think the answer is yours: if you want to calculate the electron-phonon interaction of an instable (possibly metastable) phase of a material, please do. If instead instability is soemething that troubles you, then you better settle your troubles first. Cheers - SB<div><br><div><div>On Dec 9, 2007, at 11:17 AM, Guoying Gao wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Dear everyone,<br> I intend to do the electron-phonon coupling calculation.<br>However, I found some imaginary frequencies in the phonon band<br>structure.<br>So is it reasonable to calculate the lambda for the qpoints with<br>imaginary frequencies and why?<br>Thanks very much!<br>Guoying<br>National Lab of Superhard Materials, JiLin Univ, P. R. 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