[Pw_forum] negative frequencies during phonon calculations

C.H. Hu chaohao.mse at gmail.com
Thu Oct 25 10:30:37 CEST 2007


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
============================
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