Many, MANY imaginary modes

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Hello Community,

I am attempting to optimize the geometry of several molecules that contain one aromatic ring. Additionally I am optimizing the cations and radicals that result from hydride and hydrogen atom extraction, respectively.

I am experiencing a relatively pervasive problem (about 20 of 50 molecules, give or take), that come back with many, many imaginary vibrational modes. Below is one such case for the ortho-xylenyl cation. The output geometry looks fine, however, there are 26 imaginary modes upwards of -4600 wavenumbers!

Does anyone have any thoughts or suggestions on what the problem may be?

Many thanks in advance!

Input Deck:

start molecule

charge +1

geometry noautosym
 C    0.72691046     1.45284526     0.11091742
 C   -0.63210123     0.76104776     0.13737944
 C   -0.45116581    -0.78455354    -0.02661775
 C    0.67417868    -1.30621629    -0.21286591
 C    1.90505572    -0.56823016    -0.23654556
 C    1.86346161     0.85642305    -0.07043133
 H    2.82627848     1.40454991    -0.09469476
 H    0.63615184     2.56001755     0.26219448
 H    0.80063075    -2.41913892    -0.37516601
 H    2.81868313    -1.06939078    -0.37201259
 C   -1.69675663     1.39138580     0.21239212
 H   -1.70695829     2.49124768     0.30020564
 H   -2.68461262     0.92621640     0.19099999
 C   -1.78247648    -1.56431749     0.06218713
 H   -2.50513672    -1.23943447    -0.68946057
 H   -2.24333518    -1.44725528     1.04698327
 H   -1.56210081    -2.62497023    -0.09746686
end

basis spherical
C library 6-31G*
H library 6-31G*
O library 6-31G*
END

stepper
 maxiter 200
end

dft
 xc b3lyp
 iterations 200
end

cosmo
 dielec 78.4
 rsolv 1.30
 iscren 0
 ificos 1
 lineq 0
 do_gasphase false
end

task dft optimize

task dft freq 


Output geometry:

    17

 C     0.68376808     1.46742475     0.11473114
 C    -0.54820826     0.71391884     0.12509824
 C    -0.51886043    -0.73510232    -0.02138848
 C     0.71771712    -1.32932903    -0.21902506
 C     1.89583837    -0.56414055    -0.24021652
 C     1.88854500     0.83631656    -0.06865335
 H     2.81818986     1.39499151    -0.08823833
 H     0.62709959     2.54293796     0.24839030
 H     0.78428485    -2.40350795    -0.35380689
 H     2.84577474    -1.07204553    -0.38596917
 C    -1.72183025     1.40881544     0.22039110
 H    -1.71968991     2.49114462     0.30650385
 H    -2.69407128     0.92857296     0.19436920
 C    -1.77216931    -1.55486255     0.05749062
 H    -2.50930255    -1.24529074    -0.69353053
 H    -2.24475246    -1.45032173     1.04274186
 H    -1.55225773    -2.61291862    -0.09985774


Projected Modes:

 ----------------------------------------------------------------------------
 Normal Eigenvalue ||           Projected Infra Red Intensities
  Mode   [cm**-1]  || [atomic units] [(debye/angs)**2] [(KM/mol)] [arbitrary]
 ------ ---------- || -------------- ----------------- ---------- -----------
    1    -4608.262 ||    0.616187          14.216       600.690     142.199
    2    -4479.212 ||    0.106889           2.466       104.201      24.667
    3    -3776.994 ||    0.005477           0.126         5.339       1.264
    4    -3528.245 ||    0.033900           0.782        33.047       7.823
    5    -3320.287 ||    0.074962           1.729        73.077      17.299
    6    -3242.856 ||    0.017225           0.397        16.791       3.975
    7    -2994.189 ||    0.144678           3.338       141.039      33.388
    8    -2683.759 ||    0.001751           0.040         1.707       0.404
    9    -2251.862 ||    0.000787           0.018         0.767       0.182
   10    -2062.414 ||    0.047604           1.098        46.407      10.986
   11    -1989.765 ||    0.000197           0.005         0.192       0.045
   12    -1883.087 ||    0.082451           1.902        80.377      19.027
   13    -1817.149 ||    0.041938           0.968        40.883       9.678
   14    -1732.541 ||    0.002387           0.055         2.327       0.551
   15    -1613.296 ||    0.010820           0.250        10.548       2.497
   16    -1477.257 ||    0.073749           1.701        71.895      17.019
   17    -1317.031 ||    0.000716           0.017         0.698       0.165
   18    -1258.820 ||    0.000077           0.002         0.076       0.018
   19    -1215.598 ||    0.010600           0.245        10.334       2.446
   20    -1043.645 ||    0.020820           0.480        20.296       4.805
   21     -877.968 ||    0.003398           0.078         3.313       0.784
   22     -867.706 ||    0.004100           0.095         3.997       0.946
   23     -746.045 ||    0.000384           0.009         0.374       0.089
   24     -553.902 ||    0.007930           0.183         7.731       1.830
   25     -439.702 ||    0.002706           0.062         2.638       0.625
   26     -271.939 ||    0.000889           0.021         0.867       0.205
   27       -0.000 ||    0.008560           0.197         8.344       1.975
   28       -0.000 ||    0.008501           0.196         8.287       1.962
   29        0.000 ||    0.001993           0.046         1.943       0.460
   30        0.000 ||    0.009355           0.216         9.120       2.159
   31        0.000 ||    0.001270           0.029         1.238       0.293
   32        0.000 ||    0.000862           0.020         0.840       0.199
   33      165.222 ||    0.019156           0.442        18.674       4.421
   34      693.684 ||    0.015361           0.354        14.975       3.545
   35      808.930 ||    0.004877           0.113         4.754       1.125
   36     1017.108 ||    0.001360           0.031         1.326       0.314
   37     1149.865 ||    0.005525           0.127         5.386       1.275
   38     1220.105 ||    0.002900           0.067         2.827       0.669
   39     1424.112 ||    0.004540           0.105         4.426       1.048
   40     1545.903 ||    0.017548           0.405        17.107       4.050
   41     1671.980 ||    0.016708           0.385        16.287       3.856
   42     1705.374 ||    0.005813           0.134         5.666       1.341
   43     2532.736 ||    0.002194           0.051         2.139       0.506
   44     2627.224 ||    0.025924           0.598        25.272       5.983
   45     2690.238 ||    0.015748           0.363        15.352       3.634
   46     2754.035 ||    0.125015           2.884       121.871      28.850
   47     2762.858 ||    0.149932           3.459       146.161      34.600
   48     2773.665 ||    0.066604           1.537        64.929      15.370
   49     2806.405 ||    0.168478           3.887       164.241      38.880
   50     2863.544 ||    0.149385           3.446       145.628      34.474
   51     2882.665 ||    0.069728           1.609        67.974      16.091
 ----------------------------------------------------------------------------

  • Huub Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
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Threads 1
Posts 185
Hi,

There seems to be an oversight in the code. NWChem-6.3 does not have analytical COSMO frequencies. The code should have detected that and switched to numerical frequencies but it does not do that. I have fixed this in the development version now but for the NWChem-6.3 release please use

     task dft freq numerical

That should fix this issue.

Best wishes, Huub

Clicked A Few Times
Threads 8
Posts 20
many negative frequencies
Hello Huub

I am also facing similar issues with many negative frequencies but no COSMO ....just simple ground state optimization within the latest NWChem-6.5
I tried rerunning with 'task dft freq numerical'

still the same problem persisted

Any other suggestions??

Pansy


Quote:Huub Aug 1st 12:06 pm
Hi,

There seems to be an oversight in the code. NWChem-6.3 does not have analytical COSMO frequencies. The code should have detected that and switched to numerical frequencies but it does not do that. I have fixed this in the development version now but for the NWChem-6.3 release please use

     task dft freq numerical

That should fix this issue.

Best wishes, Huub


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