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Compare vibrational frequencies for two calculations for C2N2+ (Cyanogen cation)


A = HF/6-31G*
B = MP2/6-31G*

scale factors=0.8985, 0.943 -0.206 0.237
  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   2251 2472 -220.8 0.911   12.390 12.597 0.984   0.00 0.00  
2 Σg Σg   871 971 -99.4 0.898   13.507 13.270 1.018   0.00 0.00  
3 Σu Σu   2118 1871 247.6 1.132   12.848 12.848 0.000 1.000   1851.33 10966.86 0.169
4 Πg Πg   513 605 -91.9 0.848   12.177 12.175 0.001 1.000   0.00 0.00  
5 Πg Πg   446 480 -34.3 0.929   12.177 12.175 0.001 1.000   0.00 0.00  
6 Πu Πu   218 249 -31.1 0.875   12.848 12.848 0.000 1.000   15.83 14.89 1.063
7 Πu Πu   213 165 48.0 1.290   12.848 12.848 0.000 1.000   36.00 19.07 1.888
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.