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Hello all!<br>
<br>
I am calculating the phonon dispersion curves of a monolayer of Li
(hcp).<br>
Crystal energies and electronic band structure of my calculation are in
good agreement with literature but, when I calculate phonon dispersion
curves something strange happens. <br>
<br>
I first obtain ph frequencies in symmetry points ( gamma, K and M) and
all of them seem to be alright except for the first branches at K and M
which are negative. <br>
<br>
<blockquote><small>Gamma<br>
omega( 1) = 0.268417 [THz] = -8.953502 [cm-1]</small><br>
<small> omega( 2) = 0.260430 [THz] = -8.687054 [cm-1]</small><br>
<small> omega( 3) = 0.260430 [THz] = -8.687054 [cm-1]</small><br>
<small>K<br>
omega( 1) = -2.451410 [THz] = -81.770768 [cm-1]</small><br>
<small> omega( 2) = 8.391945 [THz] = 279.927008 [cm-1]</small><br>
<small> omega( 3) = 8.391945 [THz] = 279.927008 [cm-1]</small><br>
<small>M<br>
omega( 1) = -0.453435 [THz] = -15.125059 [cm-1]</small><br>
<small> omega( 2) = 5.259870 [THz] = 175.451548 [cm-1]</small><br>
<small> omega( 3) = 9.222334 [THz] = 307.626006 [cm-1]</small><br>
</blockquote>
I don't understand at all what can be going on. <br>
Thanks a lot!<br>
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