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<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Hi</DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Thanks for your reply</DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">What i meant to say was, does not the ionicity (Born charges and ..) of the crystal, which splits the TO-LO phonons, show itself as a gap in high-energy region of the phonon DOS? If not, what is the sign of this splitting in the phonon dos diagram? </DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Thanks again</DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"> </DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">R. Ebraahimi</DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Grad. Student- Tehran Uni. <BR></DIV>
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</FONT>> Does the existence of a gap in the high-energy region of the phonon DOS > means ionicity of the crystal <BR><BR>No, does not. It means just the mass difference, i.e. one of compound componenet is rather light, than other(s), as examlpe, NiAl, FeAl, FeH, PdH, etc. <BR><BR>> (splitting of the TO and LO-like phonons)? <BR><BR>This one is more relevant for the ionicity issue. This happens in polar semiconductors/insulatoras. Another excitnig example is gamma-boron phase where a cage of B-atoms (icosahedra, B12) is charged negatively, but dumbbell B-atoms B2 are charged positively giving rise for LO-TO splitting. <BR><BR>> The higher the gap, means the more ionicity?<BR><BR>The gap depends on both the Born effective charge and static dielectric constant (see any textbook, or Rev.Mod.Phys. 73, 515, 2002, see page 527). So, the gap is the result of the competition of these parameters. <BR>I suppose analyzing this relation
for yourself will give you more insight. <BR><BR>Hope this helps.<BR><BR>Bests,<BR>Eyvaz.<BR><BR>-------------------------------------------------------------------<BR>Prof. Eyvaz Isaev, <BR>Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, <BR>Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden <BR>Condensed Matter Theory Group, Uppsala University, Sweden <BR><A href="mailto:Eyvaz.Isaev@fysik.uu.se" ymailto="mailto:Eyvaz.Isaev@fysik.uu.se">Eyvaz.Isaev@fysik.uu.se</A>, <A href="mailto:isaev@ifm.liu.se" ymailto="mailto:isaev@ifm.liu.se">isaev@ifm.liu.se</A>, <A href="mailto:eyvaz_isaev@yahoo.com" ymailto="mailto:eyvaz_isaev@yahoo.com">eyvaz_isaev@yahoo.com</A> <BR><BR><BR><BR><BR> <BR>_______________________________________________<BR>Pw_forum mailing list<BR><A href="mailto:Pw_forum@pwscf.org"
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