Thanks If we remove those parameters in vc-relax calculation then it doesnt work properly (non-zero pressure) . The scf calculation after using optimized geometry gives almost zero pressure even if I dont use those parameters (ecfixed, qcutz, q2sigma) but things change for phonon frequencies. I get negative phonon frequencies (optical) by keeping those parameters inside the scf calculation after which the phonon calculation follows. * * *Aman *
On Wed, Mar 3, 2010 at 12:28 AM, Ngoc Linh Nguyen <nnlinh at sissa.it> wrote: > Amandeep Kaur wrote: >> Hello >> >> I did vc-relax calculation for ZrNCl and I got the optimized geometry. >> Then I did a scf calculation using the relaxed coordinates and atomic >> positions and I incorporated the ecfixed, qcutz and q2sigma in the scf >> calculation. Then I did a phonon calculation using the same prefix as >> in the scf calculation ( phonon calculation follows from a scf >> calculation) and I got negative optical frequencies. > Normally, a negative optical frequency specifies a case of unstable > configuration. >> Is this due to >> the use of ecfixed, qcutz and q2sigma in the scf calculation because I >> ran one scf calculation using the optimized geometry without using the >> above parameters and did a phonon calculation following scf >> calculation and there were no negative phonon frequencies. > The problem possibly comes from non-synchronization of vc-relax and scf > calculation functional, and it could result that the optimal geometry of > vc-relax is not the optimal geometry of scf calculation. >> Are these parameters (ecfixed, qcutz and q2sigma) only to be used for >> vc-relax not for the scf calculation even if we want to use the >> optimized geometry because the pressure from the scf calculation using >> optimized geometry comes out to be small but not exactly the same as >> that of vc-relax calculation. Then the question is that should these parameters (ecfixed, qcutz and q2sigma) be used or not for scf calculations because I got negative optical phonon frequencies though I am using optimized geometry. >> >> > I suggest that you should recalculate and synchronize functional in both > vc-relax and scf, which is done by either keeping these parameters or > removing them for both calculations. > > Good luck > > Linh >> Any help will be appreciated. >> >> Thanks >> >> >> > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- Amandeep Kaur Graduate Student Department of Physics University of California,Davis -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100303/57612b19/attachment.htm
