Dear C. H.,
It would be helpful if we knew a little bit more about your system. Is it a metal? How many irreducible representations? The Eliashberg formalism for e-p interactions in metals involves a "double delta" integration over the Fermi energy dispersion at k-whatever, depends on the broadening (screening) parameter chosen, and converges excruciatingly.repeat painfully.slow. As an example, see the following page from my web site (http://www.w2agz.com/snxaps07.htm) which contains the APS March Meeting talk I gave earlier this year on my (feeble) attempt to compute the gamma-point coupling in monoclinic (24 IRs !), 300 millikelvin superconductor, polysulfur nitride, (SN)x. I used a tr2_ph = 1e-11, and you'll see the lowest two values of omega are negative (open my talk). The computation took a day on a 4-year old dual Xeon box. I figure a "serious" calculation would require tr2_ph = 1e-14 at least, or a computer on the scale of a Blue Gene. Sidebar for the ph.x developers: It would be neat to be able to set a "suspension" mid-execution flag to be able to resume a long run later (maybe even on another computer). Having said all this, Quantum-Espresso is the only free package I know that even attempts to calculate alpha-squared F(omega). Viva Italia. Regards, -Paul Paul M. Grant, PhD Principal, W2AGZ Technologies Visiting Scholar, Applied Physics, Stanford University EPRI Science Fellow (Retired) IBM Research Staff Member Emeritus <mailto:w2agz at pacbell.net> w2agz at pacbell.net <http://www.w2agz.com/> http://www.w2agz.com From: pw_forum-bounces at pwscf.org [mailto:[email protected]] On Behalf Of C.H. Hu Sent: Thursday, October 25, 2007 1:31 AM To: PWSCF Forum Subject: [Pw_forum] negative frequencies during phonon calculations 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 ============================ -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20071101/197f51da/attachment-0001.htm
