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

Compare vibrational frequencies for two calculations for HCN (Hydrogen cyanide)

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 Σ Σ   3309 3311 -2.2 0.999   1.208 1.159 0.050 1.043   60.81 63.94 -3.13 0.951
2 Σ Σ   2191 1924 267.0 1.139   4.802 5.786 -0.984 0.830   11.72 0.13 11.60 93.397
3 Π Π   797 679 118.2 1.174   1.346 1.336 0.011 1.008   38.08 38.52 -0.44 0.989
4 Π Π   797 679 118.2 1.174   1.346 1.336 0.011 1.008   38.08 38.52 -0.44 0.989
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.