[Pw_forum] matdyn.x

[Stefano de Gironcoli]

are you imposing acoustic sum rule  ? this change slightly the frequencies .
isn't strange that your frequencies are all negative (imaginary) ?
is your system stable ?
stefano


  05/11/2011 01:20 PM, S. K. S. wrote:
>   Dear All,
>
>   I find a bit strange results when using matdyn.x to perform the
> interpolation in order
>   to get  a complete phonon dispersion plot.
>
>   In case of my system, at Gamma point,  ph.x prints out two noticeably
>   distinguishable triply degenerate phonon modes of frequency values as follows :
>
>   -18.9595  -18.9595  -18.9595  -11.8835  -11.8835  -11.8835
>
>   However, after using "matdyn.x" the above phonons become like :
>
>   -18.6356  -18.6356  -18.6356  -18.6096  -18.6096  -18.6096
>
>   This looks quite strange to me.  As far as I understand, the phonon
> interpolation should
>   not change the frequency values at Gamma point or any other
> high-symmetry point
>   (suppose X in my case) which have been already computed by the
>   QE_phonon code. Interpolation means, it should only generate more
> frequencies in between
>   Gamma and X point, not changing the frequency values in the exact
>   Gamma  and X point, which have been already printed  by the ph.x run.
>
>   Looking forward to your comments.
>
>   Thanking you and with my best regards,
>
>   Saha S. K.
>   R&D Assistant,
>   JNCASR
>   Bangalore -560064
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