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


A = HF/6-31G*
B = MP2/6-31G*

scale factors=0.8985, 0.943 -0.557 -0.181 -0.164 0.274 -0.178 0.383
  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 3155 -34.7 0.989   1.125 1.125 0.000 1.000   30.97 34.90 0.887
2 A' A'   3045 3065 -20.1 0.993   1.095 1.096 -0.001 0.999   31.74 40.52 0.783
3 A' A'   3011 3035 -24.0 0.992   1.057 1.055 0.002 1.002   40.41 41.64 0.971
4 A' A'   1861 2482 -620.4 0.750   11.934 12.491 0.955   445.82 1645.56 0.271
5 A' A'   1516 1490 26.0 1.017   1.864 2.045 0.912   65.13 36.88 1.766
6 A' A'   1407 1406 1.5 1.001   1.491 1.481 0.010 1.006   58.60 14.58 4.019
7 A' A'   1234 1225 8.6 1.007   1.673 1.583 0.090 1.057   25.13 4.90 5.129
8 A' A'   1088 1113 -24.6 0.978   1.635 1.799 0.909   15.18 44.12 0.344
9 A' A'   877 888 -11.3 0.987   2.387 2.113 1.130   53.96 81.85 0.659
10 A' A'   536 591 -55.0 0.907   4.234 4.412 0.960   14.78 28.28 0.523
11 A' A'   206 221 -14.2 0.936   4.422 4.039 1.095   4.19 7.96 0.526
12 A" A"   1077 1030 47.3 1.046   1.400 1.438 -0.038 0.974   12.98 17.48 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.