Dear <span class="Apple-style-span" style="font-family: 'times new roman', 'new york', times, serif; font-size: 16px; border-collapse: collapse; ">Reza Ebraahimi:</span><div><font class="Apple-style-span" face="'times new roman', 'new york', times, serif" size="4"><span class="Apple-style-span" style="border-collapse: collapse; font-size: 16px; "><br>
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<div><div style="font-family: 'times new roman', 'new york', times, serif; font-size: 12pt; "><div>I have a question. Does the existence of a gap in the high-energy region of the phonon DOS means ionicity of the crystal (splitting of the TO and LO-like phonons)? The higher the gap, means the more ionicity?</div>
</div></div></blockquote><div>I do not think so.</div><div>You can see the "one-dimensional diatomic chain model" as given in <Dynamic Theory of Crystal Lattices> written by Max Born and Kun Huang.</div>
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</div>Hui Wang<br>School of physics, Nankai University, Tianjin, China<br>
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