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

Compare vibrational frequencies for two calculations for C2N2 (Cyanogen)

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 Σg Σg   2460 2128 332.1 1.156   12.558 12.454 0.104 1.008   0.00 0.00 0.00  
2 Σg Σg   833 818 15.2 1.019   13.313 13.432 -0.119 0.991   0.00 0.00 0.00  
3 Σu Σu   2285 1944 341.3 1.176   12.848 12.848 0.000 1.000   3.76 12.59 -8.83 0.298
4 Πg Πg   549 496 53.6 1.108   12.193 12.181 0.012 1.001   0.00 0.00 0.00  
5 Πg Πg   549 496 53.6 1.108   12.193 12.181 0.012 1.001   0.00 0.00 0.00  
6 Πu Πu   251 223 27.4 1.123   12.848 12.848 0.000 1.000   25.06 18.80 6.25 1.333
7 Πu Πu   251 223 27.4 1.123   12.848 12.848 0.000 1.000   25.06 18.80 6.25 1.333
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.