Hello, I have a suggestion that might help, since we experienced this problem before. Try to relax the structure, and especially the* atomic positions* before you start phonon calculations. Based on your optimization results also you will have better idea about your PP choices.
Good Luck IYAD 2012/1/2 ????? ???????????? <eiklm at mail.ru> > Dear QE users, > > I attempt to calculate phonon dispersion in alpha-quartz and keep getting > the wrong result. Optical branches look rather plausible, but acoustic > branches include some negative frequencies, moreover, one branch seems to > be negative in the whole Brillouin zone. I tried to use different > pseudopotentials, to select different q-grids, ecutwfc and ecutrho values, > but result remains the same. > My scf input: > > &control > calculation='scf', > restart_mode='from_scratch', > prefix='sio2', > pseudo_dir = '/home/grysha/espresso/pseudo/', > outdir='/home/grysha/espresso/tmp/' > / > &system > ibrav=4, > celldm(1)=9.289897331, > celldm(3)=1.099552482, > nat= 9, ntyp= 2, > ecutwfc = 20.0 > ecutrho = 150.0 > / > &electrons > electron_maxstep=1000 > mixing_mode = 'plain' > mixing_beta = 0.7 > conv_thr = 1.0d-8 > / > ATOMIC_SPECIES > Si 28.086 Si.pz-vbc.UPF > O 15.999 O.pz-rrkjus.UPF > ATOMIC_POSITIONS crystal > Si 0.46990000 0.00000000 0.66666667 > Si 0.00000000 0.46990000 0.33333333 > Si -0.46990000 -0.46990000 0.00000000 > O 0.41410000 0.26810000 0.78540000 > O -0.26810000 0.14600000 0.45206667 > O -0.14600000 -0.41410000 0.11873333 > O 0.26810000 0.41410000 -0.78540000 > O -0.41410000 -0.14600000 -0.11873333 > O 0.14600000 -0.26810000 -0.45206667 > K_POINTS automatic > 4 4 4 0 0 0 > > Phonon input: > > phonons of SiO_2 > &inputph > tr2_ph=1.0d-12, > prefix='sio2', > ldisp=.true., > nq1=4, nq2=4, nq3=4 > amass(1)=28.086, > amass(2)=15.999, > outdir='/home/grysha/espresso/tmp', > fildyn='sio2.dynFull', > / > > q2r input: > > &input > fildyn='sio2.dynFull', zasr='simple', flfrc='sio2444.fc' > / > > > Trying to calculate dispersion e.g. along the Gamma --- A line with such > input > > &input > asr='simple', amass(1)=28.086, amass(2)=15.999, > flfrc='sio2444.fc', flfrq='sio2.freq' > / > 11 > 0.0 0.0 0.000000 0.0 > 0.0 0.0 0.0866025 0.0 > 0.0 0.0 0.173205 0.0 > 0.0 0.0 0.259808 0.0 > 0.0 0.0 0.346410 0.0 > 0.0 0.0 0.433013 0.0 > 0.0 0.0 0.519615 0.0 > 0.0 0.0 0.606218 0.0 > 0.0 0.0 0.692820 0.0 > 0.0 0.0 0.779423 0.0 > 0.0 0.0 0.866025 0.0 > > I obtain in the sio2.freq file > > &plot nbnd= 27, nks= 11 / > 0.000000 0.000000 0.000000 > -3.9029 -1.6909 -0.9482 55.4410 58.8549 184.0277 > 232.6261 232.8523 328.4843 362.4152 372.6477 373.7721 > 424.6636 425.2693 446.6598 518.9579 681.4918 682.2090 > 775.2395 775.6317 778.7409 1081.8532 1082.0740 1096.3594 > 1172.6020 1172.7318 1231.8798 > 0.000000 0.000000 0.086602 > -27.8791 -24.0601 34.3374 57.7231 79.0905 185.5367 > 222.9925 242.2063 317.0109 365.2996 371.2517 382.6987 > 418.6292 430.0279 445.5397 521.3980 655.6902 706.8253 > 771.8412 778.2792 779.1211 1079.7256 1084.3283 1096.2590 > 1161.7487 1183.7450 1233.8392 > 0.000000 0.000000 0.173205 > -42.4501 -9.1280 61.2822 73.4236 100.4741 191.4075 > 214.2298 250.4044 293.9354 359.5278 385.7910 392.7004 > 412.1738 433.0018 442.8980 527.3652 629.0604 729.1692 > 768.1371 779.8632 780.1202 1077.7929 1086.6829 1095.9627 > 1152.2769 1193.5893 1237.5794 > 0.000000 0.000000 0.259808 > -52.8832 51.6657 77.3462 97.0335 116.7849 202.2120 > 207.1785 255.6953 266.4743 356.9882 398.4107 401.5138 > 405.7037 434.3569 440.0324 534.6626 602.8471 747.0288 > 764.9138 780.6564 780.8533 1076.3172 1088.9413 1095.4574 > 1144.7947 1202.0362 1238.6139 > 0.000000 0.000000 0.346410 > -58.6717 74.3589 85.0705 128.2999 130.9468 201.2035 > 208.4521 243.0812 255.8998 358.7639 398.8673 406.8712 > 407.6452 435.0435 437.8321 542.7959 579.1644 758.8697 > 762.7038 780.9131 781.1744 1075.3784 1091.0091 1094.6777 > 1139.5788 1210.4478 1234.1293 > 0.000000 0.000000 0.433013 > -60.8276 83.9302 87.2635 134.9317 167.8644 185.4667 > 197.4218 245.0537 249.7366 362.0234 393.8809 410.1527 > 410.7431 435.4336 436.7230 553.4463 560.5617 761.4133 > 764.3324 781.0491 781.1413 1074.9821 1092.7449 1093.5520 > 1137.1544 1220.0745 1225.2006 > 0.000000 0.000000 0.519615 > -60.1379 80.5518 86.7839 132.6697 149.3933 198.7177 > 200.3888 241.4125 253.5269 360.6371 395.7978 409.1896 > 409.5822 435.2824 437.1175 547.6607 569.0894 761.4928 > 762.8666 780.9771 781.1909 1075.1131 1091.9347 1094.1553 > 1137.9753 1215.1177 1230.0095 > 0.000000 0.000000 0.606218 > -56.3113 65.0439 82.0152 112.8013 123.3145 204.0657 > 207.4619 252.7666 256.6986 357.3738 402.2872 403.2411 > 404.9860 434.7431 438.8123 538.5747 590.4774 753.7985 > 763.6404 780.8314 781.0603 1075.7777 1090.0095 1095.1065 > 1141.8689 1206.1496 1237.0771 > 0.000000 0.000000 0.692820 > -48.3077 33.4208 70.6393 84.0546 109.2574 196.4080 > 210.5025 253.5698 280.4439 357.7446 392.5521 397.3795 > 408.9672 433.8191 441.4193 530.9458 615.7606 738.7961 > 766.4268 780.3237 780.5636 1076.9885 1087.8329 1095.7382 > 1148.2613 1197.9403 1238.6959 > 0.000000 0.000000 0.779423 > -35.4182 -25.8479 49.1690 64.6900 90.4259 187.7989 > 218.3935 246.5521 306.2412 362.0995 378.5373 387.7484 > 415.3698 431.7777 444.3207 524.1062 642.3589 718.4768 > 769.9587 779.2468 779.5653 1078.7078 1085.5161 1096.1347 > 1156.7679 1188.8888 1235.7641 > 0.000000 0.000000 0.866025 > -17.2456 -13.7809 17.5251 53.9027 67.3275 184.3786 > 227.8145 237.5840 325.1353 365.1032 368.9991 377.8392 > 421.8521 427.7529 446.3640 519.5984 668.8173 694.5999 > 773.6796 776.9999 778.8399 1080.8109 1083.1472 1096.3340 > 1167.0735 1178.3041 1232.4106 > > Single-phonon calculation at the A point also gives some negative > frequencies: > > omega( 1 - 1) = -96.6 [cm-1] --> A > omega( 2 - 2) = -69.9 [cm-1] --> A > omega( 3 - 3) = -52.9 [cm-1] --> A > omega( 4 - 4) = -25.6 [cm-1] --> A > omega( 5 - 5) = -13.8 [cm-1] --> A > omega( 6 - 6) = 169.3 [cm-1] --> A > omega( 7 - 7) = 218.6 [cm-1] --> A > omega( 8 - 8) = 227.9 [cm-1] --> A > omega( 9 - 9) = 318.1 [cm-1] --> A > omega( 10 - 10) = 360.1 [cm-1] --> A > omega( 11 - 11) = 362.7 [cm-1] --> A > omega( 12 - 12) = 371.0 [cm-1] --> A > omega( 13 - 13) = 412.5 [cm-1] --> A > omega( 14 - 14) = 419.1 [cm-1] --> A > omega( 15 - 15) = 441.1 [cm-1] --> A > omega( 16 - 16) = 524.0 [cm-1] --> A > omega( 17 - 17) = 668.1 [cm-1] --> A > omega( 18 - 18) = 694.6 [cm-1] --> A > omega( 19 - 19) = 773.0 [cm-1] --> A > omega( 20 - 20) = 776.0 [cm-1] --> A > omega( 21 - 21) = 779.8 [cm-1] --> A > omega( 22 - 22) = 1078.2 [cm-1] --> A > omega( 23 - 23) = 1080.8 [cm-1] --> A > omega( 24 - 24) = 1094.3 [cm-1] --> A > omega( 25 - 25) = 1165.6 [cm-1] --> A > omega( 26 - 26) = 1175.8 [cm-1] --> A > omega( 27 - 27) = 1244.2 [cm-1] --> A > > but I wonder that positive frequencies in these two cases are not > significantly different. > Where should I dig to avoid instability? I would be grateful for any > suggestion! > > Regards > > Mikhail Goncharovski > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- _______________________________ IYAD I. AL-QASIR, PhD Research Associate Department of Nuclear Engineering North Carolina State University Campus Box 7909 2500 Stinson Dr. Raleigh, NC 27695-7909 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120102/d1cea43b/attachment-0001.htm
