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

Compare vibrational frequencies for two calculations for C2H3 (vinyl)

A = HF/6-31G*

B = MP2FC/6-31G*

  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 A1 A1   3228 3243 -15.1 0.995   1.250 1.221 0.029 1.023   0.10 0.08 0.02 1.311
2 A1 A1   2916 2899 16.2 1.006   1.057 1.060 -0.003 0.997   168.03 297.68 -129.65 0.564
3 A1 A1   1932 1847 85.2 1.046   3.604 3.868 -0.264 0.932   9.68 5.78 3.89 1.673
4 A1 A1   1238 1149 89.1 1.078   1.075 1.058 0.017 1.016   52.04 90.96 -38.91 0.572
5 B1 B1   953 809 143.6 1.178   1.279 1.234 0.045 1.037   100.17 164.12 -63.95 0.610
6 B1 B1   774 710 64.7 1.091   1.087 1.084 0.003 1.003   141.58 132.76 8.82 1.066
7 B2 B2   3118 3148 -29.3 0.991   1.085 1.086 -0.000 1.000   399.80 405.87 -6.08 0.985
8 B2 B2   1220 1264 -44.5 0.965   1.072 1.034 0.038 1.037   5.71 10.82 -5.11 0.528
9 B2 B2   464 601 -136.4 0.773   1.100 1.684 -0.584 0.653   29.96 31.42 -1.46 0.954
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.