Many large negative frequencies


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These are the frequencies I just got running NWChem 6.6 on a slightly modified input file


 Normal Eigenvalue ||           Projected Infra Red Intensities
  Mode   [cm**-1]  || [atomic units] [(debye/angs)**2] [(KM/mol)] [arbitrary]
 ------ ---------- || -------------- ----------------- ---------- -----------
    1       -0.000 ||    0.000097           0.002         0.095       0.014
    2       -0.000 ||    0.000201           0.005         0.196       0.028
    3        0.000 ||    0.002064           0.048         2.012       0.290
    4        0.000 ||    0.001175           0.027         1.145       0.165
    5        0.000 ||    0.001426           0.033         1.391       0.201
    6        0.000 ||    0.000391           0.009         0.381       0.055
    7       37.102 ||    0.007832           0.181         7.635       1.102
    8       48.020 ||    0.003671           0.085         3.579       0.516
    9       66.766 ||    0.005664           0.131         5.521       0.797
   10       92.666 ||    0.004570           0.105         4.455       0.643
   11       99.916 ||    0.015438           0.356        15.050       2.172
   12      141.665 ||    0.011799           0.272        11.503       1.660
   13      144.708 ||    0.062446           1.441        60.876       8.784
   14      175.931 ||    0.029784           0.687        29.035       4.189
   15      211.790 ||    0.014689           0.339        14.320       2.066
   16      236.120 ||    0.007759           0.179         7.564       1.091
   17      252.995 ||    0.007173           0.165         6.993       1.009
   18      263.861 ||    0.003710           0.086         3.616       0.522
...


Here is the input file


start NbOH3_SiOH3_Na_n_c1_freqM06-L

geometry
o    -1.53818182   1.66045046  -1.06002635
nb   -0.09296080   0.79146972  -0.45379073
o     0.48976383   2.37543521   0.81035634
o    -0.25640017  -0.59787257   1.14433264
si   -0.14219494  -2.00822934   0.35615132
o     1.23631740  -2.93021375   0.46511435
o    -0.09474250  -1.36466582  -1.25244096
o     1.58416873   0.96308517  -1.54213781
o    -1.39763583  -3.08430971   0.55842462
h     2.22591749   1.60330438  -1.21649499
h     0.57626745   2.09567663   1.72584033
h    -2.22555113  -2.66871873   0.81107060
h     0.62679400  -1.64730735  -1.82436360
h     1.10101718  -3.78066689   0.88904771
na   -1.15209656   3.57930854  -0.06139465
end

basis spherical
O library aug-cc-pvdz
H library aug-cc-pvdz
Si library aug-cc-pvdz
Na library aug-cc-pvdz
Nb library LANL2DZ_ECP
end

ecp
Nb library LANL2DZ_ECP
end

driver
maxiter 500
end

dft
XC M06-L
maxiter 500
grid fine
convergence energy 1d-8
mult 2
end

task dft optimize
task dft freq