Dear all, Sorry to ask so many questions about computing phonon frequencies but recently i have got some strange results for one of the systems I am working on. My work involves computing phonon frequencies for a 42 carbon at the Gamma point so in total 126 irreducible representations. in a previous calculations, my input was: SCF FILE
/ &system ibrav= 0, celldm(1) =1.88972599, nat=42, ntyp= 1, ecutwfc =32, ecutrho=128, occupations='smearing', smearing='mp',degauss=0.01 / &electrons conv_thr=1.D-6, mixing_beta=0.7D0, diago_david_ndim=2, ATOMIC_SPECIES C 12.0107 C.pbe-rrkjus.UPF ... PH FILE: Phonon calculation for GB60 at gamma point &inputph tr2_ph=1.0d-15, prefix='GrBo42ph', fildvscf='GB60dvscf', elph=.true.,..... The results obtained were: omega( 1) = -4.450324 [THz] = -148.446823 [cm-1] omega( 2) = -3.144068 [THz] = -104.874835 [cm-1] omega( 3) = 2.963314 [THz] = 98.845504 [cm-1] omega( 4) = 3.454797 [THz] = 115.239637 [cm-1] omega( 5) = 3.908880 [THz] = 130.386191 [cm-1]... omega(**) = 47.380063 [THz] = 1580.428796 [cm-1] omega(**) = 47.573318 [THz] = 1586.875087 [cm-1] omega(**) = 47.821300 [THz] = 1595.146853 [cm-1] omega(**) = 48.119632 [THz] = 1605.098137 [cm-1] Where the 2 negative frequencies,as professor Gionazzi repeated several times, could be due to the violation of the ASR rule. For my own piece of mind I repeated the calculation with a better accuracy where ecutrho=256 (8 times ecutwfc which should be the case if an ultrasoft potential is used)and tr2_ph =10^(-17) although mixing_beta was set equal to 0.3 this time. I expected better results but what I got was the following: omega( 1 - 1) = -77614121.2 [cm-1] --> A' I+R omega( 2 - 2) = -13157144.1 [cm-1] --> A' I+R omega( 3 - 3) = -5577066.3 [cm-1] --> A' I+R omega( 4 - 4) = -4332492.8 [cm-1] --> A' I+R omega( 5 - 5) = -4094962.7 [cm-1] --> A' I+R omega( 6 - 6) = -3368158.6 [cm-1] --> A' I+R omega( 7 - 7) = -2781643.0 [cm-1] --> A' I+R omega( 8 - 8) = -2403295.2 [cm-1] --> A' I+R omega( 9 - 9) = -1777809.3 [cm-1] --> A' I+R omega( 10 - 10) = 82.5 [cm-1] --> A'' I+R omega( 11 - 11) = 85.8 [cm-1] --> A'' I+R... omega(120 -120) = 2301243.8 [cm-1] --> A' I+R omega(121 -121) = 2494732.0 [cm-1] --> A' I+R omega(122 -122) = 2788571.0 [cm-1] --> A' I+R omega(123 -123) = 3135326.3 [cm-1] --> A' I+R omega(124 -124) = 3630869.3 [cm-1] --> A' I+R omega(125 -125) = 8808450.4 [cm-1] --> A' I+R What is the reason for those LARGE negative values at the beginning and the LARGE ones at the end? Is it because mixing_beta was changed? Thanks for the help Elie KoukaesUniversity of NottinghamNG7 2RDUK -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20120902/ea1e7fd9/attachment-0002.html