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

Compare vibrational frequencies for two calculations for CCH2 (vinylidene)

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   2989 3024 -34.7 0.989   1.066 1.065 0.001 1.001   21.20 46.33 -25.13 0.458
2 A1 A1   1660 1611 49.4 1.031   5.594 6.218 -0.624 0.900   63.17 79.48 -16.31 0.795
3 A1 A1   1268 1385 -116.1 0.916   3.487 1.151 2.336 3.030   8.86 5.36 3.50 1.653
4 B1 B1   833 898 -64.6 0.928   1.337 1.346 -0.008 0.994   95.71 36.86 58.85 2.597
5 B2 B2   3065 3110 -45.1 0.986   1.113 1.111 0.001 1.001   5.18 19.57 -14.39 0.265
6 B2 B2   983 989 -6.1 0.994   1.312 1.327 -0.016 0.988   0.52 2.87 -2.35 0.181
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.