[Pw_forum] matdyn.x

S. K. S. sks.jnc at gmail.com
Wed May 11 13:20:06 CEST 2011

 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,
 Bangalore -560064

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