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III.G.7. (XIII.B.3.) (XIII.D.5.)

Compare vibrational frequencies for two calculations for C3H3N+ (acrylonitrile cation)

A = HF/6-31G*

B = MP2/6-31G*

scale factors=0.8985, 0.943
  symmetry   frequency (cm-1)   reduced mass (amu)   IR Intensity (km mol-1)
mode number A B   A B diff. ratio   A B diff. ratio   A B diff. ratio
1 A' A'   3120 3154 -33.9 0.989   1.125 1.125 0.000 1.000   30.97 34.93 -3.96 0.887
2 A' A'   3045 3064 -19.1 0.994   1.095 1.096 -0.001 0.999   31.74 40.51 -8.77 0.784
3 A' A'   3011 3035 -23.3 0.992   1.057 1.055 0.002 1.002   40.41 41.68 -1.27 0.970
4 A' A'   1861 2481 -620.0 0.750   11.934 12.490 -0.556 0.955   445.82 1644.94 -1199.11 0.271
5 A' A'   1516 1490 26.1 1.018   1.864 2.044 -0.180 0.912   65.13 36.88 28.26 1.766
6 A' A'   1407 1406 1.4 1.001   1.491 1.481 0.010 1.007   58.60 14.59 44.01 4.017
7 A' A'   1234 1225 8.6 1.007   1.673 1.583 0.090 1.057   25.13 4.86 20.27 5.173
8 A' A'   1088 1113 -24.8 0.978   1.635 1.800 -0.165 0.908   15.18 44.08 -28.91 0.344
9 A' A'   877 888 -11.5 0.987   2.387 2.113 0.274 1.130   53.96 81.83 -27.86 0.659
10 A' A'   536 591 -55.4 0.906   4.234 4.417 -0.184 0.958   14.78 28.27 -13.49 0.523
11 A' A'   206 221 -14.9 0.932   4.422 4.037 0.384 1.095   4.19 7.97 -3.79 0.525
12 A" A"   1077 1030 47.1 1.046   1.400 1.438 -0.038 0.974   12.98 17.48 -4.49 0.743
scaled by     0.8985 0.943

See section III.C.1 List or set vibrational scaling factors to change the scale factors used here.
See section III.C.2 Calculate a vibrational scaling factor for a given set of molecules to determine the least squares best scaling factor.