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Compare vibrational frequencies for two calculations for KCN (Potassium 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   2191 1938 253.3 1.131   12.831 12.824 0.007 1.001   1.36 9.88 0.138
2 Σ Σ   257 275 -18.2 0.934   17.763 17.776 -0.013 0.999   62.05 56.12 1.106
3 Π Π   65 85 -20.2 0.762   12.695 12.697 -0.002 1.000   8.49 12.01 0.707
4 Π Π   65 85 -20.2 0.762   12.695 12.697 -0.002 1.000   8.49 12.01 0.707
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.