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

Compare vibrational frequencies for two calculations for C4H9NO (Butanamide)

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   3561 3538 22.9 1.006   1.105 1.104 0.002 1.001   49.25 39.71 9.54 1.240
2 A A   3446 3411 35.3 1.010   1.047 1.046 0.001 1.001   52.62 46.54 6.08 1.131
3 A A   2949 3012 -63.1 0.979   1.104 1.103 0.001 1.001   68.15 39.96 28.18 1.705
4 A A   2935 3010 -75.5 0.975   1.100 1.103 -0.003 0.997   58.83 31.24 27.59 1.883
5 A A   2915 2993 -77.5 0.974   1.101 1.103 -0.002 0.998   21.61 0.76 20.85 28.495
6 A A   2904 2956 -51.3 0.983   1.069 1.099 -0.030 0.973   14.09 11.74 2.35 1.200
7 A A   2896 2947 -51.5 0.983   1.098 1.066 0.033 1.031   18.41 15.81 2.60 1.165
8 A A   2872 2923 -50.9 0.983   1.042 1.036 0.005 1.005   41.66 22.08 19.59 1.887
9 A A   2865 2907 -41.6 0.986   1.059 1.061 -0.002 0.998   15.29 11.19 4.10 1.366
10 A A   1778 1711 66.9 1.039   9.641 8.474 1.167 1.138   379.35 229.99 149.36 1.649
11 A A   1615 1568 46.7 1.030   1.224 1.250 -0.027 0.978   130.37 107.85 22.52 1.209
12 A A   1485 1481 3.6 1.002   1.089 1.077 0.012 1.011   3.86 5.65 -1.79 0.683
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.