[Pw_forum] negative frequencies during phonon calculations
Katalin Gaal-Nagy
katalin.gaal-nagy at physik.uni-regensburg.de
Thu Oct 25 10:45:22 CEST 2007
Dear C. H. Hu,
it depends on your system.
If you treat, e.g., a molecule, the first six frequencies should vanish.
However, due to convergence (number of plane waves, size of the supercell,
etc. ) they often appear as imaginary or small real, even if all other
frequencies are converged with respect to ecut and celldm.
If you have a bulk structure, then imaginary frequencies indicate a
lattice instability. However, they can appear also as a result of a
non-converged groundstate (Ecut, #k, ...).
Recently I also found that the parameters tr2_ph for the phonons and
conv_thr for the groundstate can affect the quality of the phonon
calculation, especially the "vanishing" frequencies for molecules.
I hope it helps.
All the best,
Katalin
On Thu, 25 Oct 2007, C.H. Hu wrote:
> Dear Pwscf users,
>
> I performed gamma-point phonon calculation for my system only including some
> light elements. Some negative frequencies appear as following. The
> structure has been optimized first and the nscf calculation was also
> performed. Does the negative frequencies indicate the structural
> instability? or how to eliminate these imaginary frequencies during my
> following calculations?
>
> =========
> q = ( 0.000000000 0.000000000 0.000000000 )
>
> **************************************************************************
> omega( 1) = -3.014004 [THz] = -100.537026 [cm-1]
> omega( 2) = -1.833969 [THz] = -61.175042 [cm-1]
> omega( 3) = -1.568539 [THz] = -52.321189 [cm-1]
> omega( 4) = -1.362118 [THz] = -45.435661 [cm-1]
> omega( 5) = -0.979698 [THz] = -32.679419 [cm-1]
> omega( 6) = 3.631786 [THz] = 121.144148 [cm-1]
> omega( 7) = 4.565661 [THz] = 152.295057 [cm-1]
> omega( 8) = 4.870748 [THz] = 162.471753 [cm-1]
> omega( 9) = 5.926574 [THz] = 197.690558 [cm-1]
> omega(10) = 6.692205 [THz] = 223.229420 [cm-1]
> omega(11) = 6.751437 [THz] = 225.205202 [cm-1]
> omega(12) = 7.152446 [THz] = 238.581500 [cm-1]
> omega(13) = 7.290775 [THz] = 243.195689 [cm-1]
> omega(14) = 7.583548 [THz] = 252.961623 [cm-1]
> omega(15) = 7.848509 [THz] = 261.799816 [cm-1]
> omega(16) = 8.216032 [THz] = 274.059149 [cm-1]
> omega(17) = 8.450907 [THz] = 281.893782 [cm-1]
> omega(18) = 8.617843 [THz] = 287.462209 [cm-1]
> omega(19) = 8.874576 [THz] = 296.025963 [cm-1]
> omega(20) = 9.106260 [THz] = 303.754152 [cm-1]
> omega(21) = 9.776634 [THz] = 326.115571 [cm-1]
> omega(22) = 9.846084 [THz] = 328.432188 [cm-1]
> omega(23) = 10.441744 [THz] = 348.301414 [cm-1]
> omega(24) = 10.901272 [THz] = 363.629712 [cm-1]
> omega(25) = 11.120174 [THz] = 370.931537 [cm-1]
> omega(26) = 11.296950 [THz] = 376.828190 [cm-1]
> omega(27) = 11.744897 [THz] = 391.770187 [cm-1]
> omega(28) = 11.823415 [THz] = 394.389308 [cm-1]
> omega(29) = 12.284723 [THz] = 409.776965 [cm-1]
> omega(30) = 12.879001 [THz] = 429.600078 [cm-1]
> omega(31) = 13.104238 [THz] = 437.113223 [cm-1]
> omega(32) = 13.295358 [THz] = 443.488354 [cm-1]
> omega(33) = 13.386218 [THz] = 446.519146 [cm-1]
> omega(34) = 13.536055 [THz] = 451.517199 [cm-1]
> omega(35) = 13.571174 [THz] = 452.688634 [cm-1]
> omega(36) = 14.064683 [THz] = 469.150452 [cm-1]
> omega(37) = 14.556450 [THz] = 485.554120 [cm-1]
> omega(38) = 14.667300 [THz] = 489.251729 [cm-1]
> omega(39) = 15.110352 [THz] = 504.030430 [cm-1]
> omega(40) = 15.395285 [THz] = 513.534849 [cm-1]
> omega(41) = 16.043631 [THz] = 535.161476 [cm-1]
> omega(42) = 16.936124 [THz] = 564.932033 [cm-1]
> omega(43) = 18.733204 [THz] = 624.876561 [cm-1]
> omega(44) = 18.876424 [THz] = 629.653928 [cm-1]
> omega(45) = 19.992373 [THz] = 666.878205 [cm-1]
> omega(46) = 21.505666 [THz] = 717.356559 [cm-1]
> omega(47) = 21.617840 [THz] = 721.098322 [cm-1]
> omega(48) = 22.309307 [THz] = 744.163333 [cm-1]
> omega(49) = 23.662551 [THz] = 789.303000 [cm-1]
> omega(50) = 24.061062 [THz] = 802.595969 [cm-1]
> omega(51) = 24.064277 [THz] = 802.703198 [cm-1]
> omega(52) = 25.648159 [THz] = 855.536168 [cm-1]
> omega(53) = 26.862084 [THz] = 896.028637 [cm-1]
> omega(54) = 26.984089 [THz] = 900.098318 [cm-1]
> omega(55) = 28.413367 [THz] = 947.774196 [cm-1]
> omega(56) = 28.483349 [THz] = 950.108578 [cm-1]
> omega(57) = 28.903442 [THz] = 964.121470 [cm-1]
> omega(58) = 29.425892 [THz] = 981.548629 [cm-1]
> omega(59) = 29.797340 [THz] = 993.938893 [cm-1]
> omega(60) = 30.194172 [THz] = 1007.175875 [cm-1]
> omega(61) = 30.533468 [THz] = 1018.493632 [cm-1]
> omega(62) = 30.805908 [THz] = 1027.581303 [cm-1]
> omega(63) = 31.041973 [THz] = 1035.455634 [cm-1]
> omega(64) = 32.094778 [THz] = 1070.573675 [cm-1]
> omega(65) = 33.759643 [THz] = 1126.107965 [cm-1]
> omega(66) = 33.969486 [THz] = 1133.107616 [cm-1]
> omega(67) = 36.434092 [THz] = 1215.318565 [cm-1]
> omega(68) = 36.726631 [THz] = 1225.076683 [cm-1]
> omega(69) = 39.522021 [THz] = 1318.321478 [cm-1]
> omega(70) = 39.623203 [THz] = 1321.696562 [cm-1]
> omega(71) = 40.034020 [THz] = 1335.400026 [cm-1]
> omega(72) = 40.044563 [THz] = 1335.751729 [cm-1]
> omega(73) = 50.292137 [THz] = 1677.576257 [cm-1]
> omega(74) = 50.298606 [THz] = 1677.792065 [cm-1]
> omega(75) = 51.050051 [THz] = 1702.857719 [cm-1]
> omega(76) = 51.176742 [THz] = 1707.083716 [cm-1]
> omega(77) = 53.131701 [THz] = 1772.294552 [cm-1]
> omega(78) = 53.564853 [THz] = 1786.743033 [cm-1]
> omega(79) = 53.946325 [THz] = 1799.467683 [cm-1]
> omega(80) = 54.547644 [THz] = 1819.525644 [cm-1]
> omega(81) = 55.855114 [THz] = 1863.138433 [cm-1]
> omega(82) = 56.009839 [THz] = 1868.299538 [cm-1]
> omega(83) = 56.878920 [THz] = 1897.289172 [cm-1]
> omega(84) = 56.962499 [THz] = 1900.077075 [cm-1]
> omega(85) = 57.147227 [THz] = 1906.238980 [cm-1]
> omega(86) = 57.294672 [THz] = 1911.157244 [cm-1]
> omega(87) = 58.113524 [THz] = 1938.471399 [cm-1]
> omega(88) = 58.186280 [THz] = 1940.898280 [cm-1]
> omega(89) = 60.420046 [THz] = 2015.409202 [cm-1]
> omega(90) = 60.431210 [THz] = 2015.781574 [cm-1]
> **************************************************************************
> =========
>
> Regards,
> C.H.
>
> --
> ============================
> C.H. Hu
> Postdoctoral fellow
> Chimie et Physico-Chimie appliquees
> Institut Francais du Petrole (IFP)
> Rueil-Malmaison, France
> E_mail: chaohao.mse at gmail.com
> ============================
>
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
, >>>>>>> Katalin Gaal-Nagy <<<<<<< ,
, Phys.Dept./INFM ,
, University of Milan ,
, Via Celoria 16 ,
, +39 02 50317377 ,
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
, >>>>>>> katalin.gaal-nagy at physik.uni-regensburg.de <<<<<<< ,
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
, >>>>>>> Don't dream your life, live your dream <<<<<<< ,
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
More information about the users
mailing list