[Pw_forum] imaginary phonon frequency for different degauss
Dear all? I am calculating phonon with QE-5.0.1. A 20x20x10 k-mesh is used in scf calculation. Phonon wave vectors are sampled on 10x10x5 mesh. But when I set degauss=0.03Ry in scf run, a imaginary frequency was found for the first branch with omega= -105.6 cm^-1 at wave vector (0.2, 0.346410162, 0.0). But if degauss=0.05Ry in scf run, this imaginary frequency disappear and become 132.1 cm^-1. Meanwhile, the frequencies of all other branches change slightly for these two degauss values. So my question is which results should I trust, degauss=0.03 Ry or 0.05Ry? Btw: both lattice parameters and the inner coordinates of atoms are well relaxed for different degauss values. I am greatly indebted to you for your help. Thanks again! Best Miao Gao --- Ph.D. student of Department of Physics, Renmin University of China. --- -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130622/201a68f4/attachment.html
[Pw_forum] imaginary phonon frequency for different degauss
Without info. about smearing method, it is hard to tell. Some methods may give you incorrect forces, resulting in incorrect phonon. degauss and k-point mesh should be well tested TOGETHER. Check out the following: http://caribeictp.uis.edu.co/lectures/R.Gebauer/Gebauer_Course2_KpointsMetals.pdf Duy Le Postdoctoral Associate Department of Physics University of Central Florida. Website: http://www.physics.ucf.edu/~dle On Sat, Jun 22, 2013 at 9:05 AM, Miao Gao wrote: > Dear all? > > I am calculating phonon with QE-5.0.1. > A 20x20x10 k-mesh is used in scf calculation. Phonon wave vectors are > sampled > on 10x10x5 mesh. But when I set degauss=0.03Ry in scf run, a imaginary > frequency > was found for the first branch with omega= -105.6 cm^-1 at wave vector (0.2, > 0.346410162, 0.0). > But if degauss=0.05Ry in scf run, this imaginary frequency disappear and > become 132.1 cm^-1. > Meanwhile, the frequencies of all other branches change slightly for these > two degauss values. > So my question is which results should I trust, degauss=0.03 Ry or 0.05Ry? > > Btw: both lattice parameters and the inner coordinates of atoms are well > relaxed for > different degauss values. > > I am greatly indebted to you for your help. Thanks again! > > Best > Miao Gao > > --- > Ph.D. student of Department of Physics, > Renmin University of China. > --- > > > > > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum
[Pw_forum] Imaginary phonon frequency
Your description is too vague. If you correctly transform your dynamical matrix to real space and use them to calculate phonons at the original wavevectors, you should get exactly the same numbers. Do you? P, > I used nq1 = 4, nq2 = 4, nq3 = 1 to do a phonon calculation. The > resulting inequivalent number of q points is 6 [...]. After a phonon > calculation, all frequencies at these 6 points are real and reasonable > [...] However, when I used these data to get a full phonon dispersion > in the first BZ. I found that some q points have imaginary > frequencies. > Can someone tell me the possible reasons? > -- Paolo Giannozzi, IOM-Democritos and University of Udine, Italy
[Pw_forum] Imaginary phonon frequency
Hi, Follow this link... http://www.quantum-espresso.org/?page_id=366#7.3 Also, are you sure that nq1 = 4, nq2 = 4, nq3 = 1 span your IBZ ? with regards, == Sonu Kumar Phd Student, Physics Department Indian Institute of Technology, Delhi-110016, India mail: 1009ukumar at gmail.com web:-http://www.iitd.ac.in/ == On Mon, Nov 12, 2012 at 5:17 AM, Caloma Trumica wrote: > Dear All, > > I used nq1 = 4, nq2 = 4, nq3 = 1 to do a phonon calculation. The resulting > inequivalent number of q points is 6. > > After a phonon calculation, all frequencies at these 6 points are real and > reasonable. > > However, when I used these data to get a full phonon dispersion in the > first BZ. I found that some q points have imaginary frequencies. > > Can someone tell me the possible reasons? > > Thank you. > > Andy > > ___ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20121112/4a6e2cec/attachment.html
[Pw_forum] Imaginary phonon frequency
Dear All, I used nq1 = 4, nq2 = 4, nq3 = 1 to do a phonon calculation. The resulting inequivalent number of q points is 6. After a phonon calculation, all frequencies at these 6 points are real and reasonable. However, when I used these data to get a full phonon dispersion in the first BZ. I found that some q points have imaginary frequencies. Can someone tell me the possible reasons? Thank you. Andy -- next part -- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/2012/3db056b4/attachment.html
