[Pw_forum] 回复： Re: [Pw_forum] negtive values for TA when using q2r.x

[li yan]

      Dear katalin,
      
      I want to find the reason of the phase transiton for AgF by calculating the phonon dispersion curves. My intent is finding the soft  mode at high pressure.
    
  >Which was the first grid, which you used to calculate the dispersion?

      AgF is fcc strcture, c/a is 1, so the mesh was initially chosen as 4*4*4. 
   
  At 3GPa, after calculating the eight special points, i found only one of them (0,0,1) has a negative mode.   Then  i did the calculation  of the phonon disperion curves with q2r.x, the frequences of TA near the gama point  are negtive.  Near gama point, i just selected one q, whose TA is negtive,  to calculate the phonon, but the value of the TA is positive. I thought  the q mesh is  small, so i chose 6*6*6 mesh. 
   
  > Does the 6x6x6 mesh include also the points you calculated for checking. 

      The 6*6*6 mesh dosen't include the above  modes which has negtive values, but i cannot find other ways to avoid the unexpected negtive values. 
   
  thank you for your advice.
    best regards
     Li Yan
  
 




		
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