Try to increase the number of k points and let us know what happens. If, as I guess, the zone-center acoustic modes soften, try to understand why, starting from the early literature on DFPT. A good starting point could be e.g., http://link.aps.org/doi/10.1103/PhysRevB.33.7017 and http://link.aps.org/doi/10.1103/PhysRevLett.62.2853 . Hope this helps Stefano Baroni
On Jul 2, 2011, at 12:02 PM, mayank gupta wrote: > Thanks Sir for your response. > > I am doing all these calculations for oxides. for example I have done > the phonon calculations for Cu2O and Ag2O system the details are as > follow > > Ag2O ecutwfc 70 Ry. Mesh (8x8x8) zone ceneter acoustic > mode=1.6 THz (with PBE) > Cu2O ecutwfc 95 Ry. Mesh (8x8x8) zone centre acoustic mode = > 1.33 THz (PW) > > I have performed above calculation using tr2_ph=1.0e-14, but the > values are almost same. the ecutrho=20times of ecutwfc. > > > Mayank > > >> Dear Mayanka, >> >> is this a polar material? If so, the violation of the ASR may be justified >> by the use of too coarse a k-point mesh. Please, provide more details on the >> system and the calculations you are doing. >> >> SB >> >> On Jul 1, 2011, at 6:17 AM, mayank gupta wrote: >> >>> Dear All >>> I have a query ragrdin phonon calculations at q=0. When I performed >>> the phonon caclualtion at q=0, we didn't get zero enrgy for acoustic >>> branches, however they can be set to zero by using acoustic/ crystal >>> sum rules. My question is if the zone center acoustic braches values >>> are too large (4 THz) even we have implemented very high convergence, >>> it is ok to apply ASR. >>> >>> Thanks >>> >>> -- >>> Mayank > > > BHABHA ATOMIC RESEARCH CENTER > MUMBAI, INDIA > Office: 022-25595606 > Home: 9920397437 / 9869834437 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110702/96cc1fd5/attachment.htm
