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

Compare vibrational frequencies for two calculations for HNO2 (Nitrous acid)

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 A' A'   3667 3489 178.3 1.051   1.067 1.066 0.001 1.001   124.75 78.91 45.84 1.581
2 A' A'   1837 2881 -1044.8 0.637   10.382 11.233 -0.851 0.924   152.17 3048.57 -2896.40 0.050
3 A' A'   1361 1244 116.6 1.094   1.286 1.307 -0.020 0.984   262.73 198.58 64.15 1.323
4 A' A'   1149 1109 40.1 1.036   14.399 6.488 7.911 2.219   203.16 27.29 175.88 7.445
5 A' A'   710 672 37.9 1.056   7.797 6.204 1.592 1.257   19.60 6.30 13.30 3.112
6 A" A"   689 570 118.5 1.208   1.179 1.159 0.020 1.017   157.55 120.05 37.50 1.312
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.