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the electristatic interaction at the origin of LO-TO splitting is
always present...<br>
<br>
for any q<>0 (even very small) it is included in the
calculation.<br>
<br>
in the limit of q->0 in non-metallic systems it gives origin to a
non analytic behavior that must be calculate separately.<br>
<br>
If you want to Fourier interpolate the phonon dispersions calculated
on a regular grid of q-points<br>
you are in trouble because non analyticity of the phonon dispersion
implyes long-range (1/R^3) interatomic force constants and so you
need to <br>
<br>
1) evaluate Z* and epsilon_infty in the limit of q->0 that
determine the non-analyticity<br>
2) remove from dynamical matrix in every q point in you grid an
electrostatic model that gives the correct non-analyticity for
q->0 and is smooth elsewhere<br>
3) Fourier interpolate the modified (hopefully short-range)
dynamical matrices <br>
4) add back the model in any q-point you want to study.<br>
<br>
This is what the sequence ph.x -> q2r.x -> matdyn.x does (in
example06 for instance) <br>
<br>
thete is some discussion of these issues in Review of Modern Physics
73, 515 (2001) and in Phys Rev 43, 7231 (1991)<br>
<br>
stefano <br>
<br>
On 04/29/2011 05:05 AM, xirainbow wrote:
<blockquote
cite="mid:BANLkTimgkd0gXKy9g+P4MXG-tveoOGAP_A@mail.gmail.com"
type="cite">
<pre wrap="">Dear Eyvaz:
Thank you very much;)
</pre>
<blockquote type="cite">
<pre wrap="">Is there LO-TO splitting far away from Gamma point?
No.
</pre>
</blockquote>
<pre wrap="">
Does LO-TO splitting must disappear at the boundary of Brillouin zone?
</pre>
<pre wrap="">
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