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Compare vibrational frequencies for two calculations for LiCN (lithium 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   2220 1955 265.5 1.136   12.805 12.784 0.021 1.002   1.83 28.82 0.063
2 Σ Σ   572 589 -17.0 0.971   7.793 7.801 -0.008 0.999   132.32 114.10 1.160
3 Π Π   162 146 16.4 1.113   11.162 11.095 0.067 1.006   41.41 45.55 0.909
4 Π Π   162 146 16.4 1.113   11.162 11.095 0.067 1.006   41.41 45.55 0.909
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.