[Pw_forum] LO-TO splitting in dynmat.x
Stefano de Gironcoli
degironc at sissa.it
Fri Apr 29 09:16:13 CEST 2011
the electristatic interaction at the origin of LO-TO splitting is always
present...
for any q<>0 (even very small) it is included in the calculation.
in the limit of q->0 in non-metallic systems it gives origin to a non
analytic behavior that must be calculate separately.
If you want to Fourier interpolate the phonon dispersions calculated on
a regular grid of q-points
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
1) evaluate Z* and epsilon_infty in the limit of q->0 that determine the
non-analyticity
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
3) Fourier interpolate the modified (hopefully short-range) dynamical
matrices
4) add back the model in any q-point you want to study.
This is what the sequence ph.x -> q2r.x -> matdyn.x does (in example06
for instance)
thete is some discussion of these issues in Review of Modern Physics 73,
515 (2001) and in Phys Rev 43, 7231 (1991)
stefano
On 04/29/2011 05:05 AM, xirainbow wrote:
> Dear Eyvaz:
> Thank you very much;)
>
>> Is there LO-TO splitting far away from Gamma point?
>> No.
>>
> Does LO-TO splitting must disappear at the boundary of Brillouin zone?
>
>
>
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