[Pw_forum] Weird jump in phonon dispersion at Gamma point

[Yao Yao]

Dear All,

I calculated a orthorhombic cell with alternating AlSb/InAs mono {110} atom 
layers with QE 4.3.2. I noticed that my phonon dispersion results were with 
steps at Gamma point for some optical branches. Looks you will get different 
frequency at Gamma when you approach Gamma from different direction (X->Gamma, 
Y->Gamma and Z->Gamma). One picture showing this is uploaded to
http://www.picvalley.net/v.php?p=u/2753/176658145760478725413524194617CoVRtxOq5iqZ20Wa3iK.PNG

Looks this is similar to the problem reported here
http://www.democritos.it/pipermail/pw_forum/2009-June/013250.html
But seems that problem has been solved according to the following email. Is 
this another problem in q2r or matdyn?

The cell was optimised to
ATOMIC_POSITIONS alat
 Al      -0.025264682   0.000000000   0.000000000
 In       0.700737593   0.479363399   0.476965330
 Sb       0.322108083   0.479363399   0.000000000
 As       1.029274264   0.000000000   0.476965330
CELL_PARAMETERS
1.351237   0.000000   0.000000
0.000000   0.958727   0.000000  
0.000000   0.000000   0.953931

Thank you very much.

Regards,
Yao