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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 = MP2FC/6-31G*

  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 2471 -10.9 0.996   12.558 12.596 -0.038 0.997   0.00 0.00 0.00  
2 Σg Σg   871 971 -99.8 0.897   13.507 13.270 0.237 1.018   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   549 605 -55.6 0.908   12.193 12.175 0.018 1.001   0.00 0.00 0.00  
5 Πu Πu   251 250 1.0 1.004   12.848 12.848 0.000 1.000   25.06 14.89 10.17 1.683
6 Πu Πu   218 250 -31.8 0.873   12.848 12.848 0.000 1.000   15.83 14.89 0.94 1.063
7 Πu Πu   213 223 -9.9 0.956   12.848 12.848 0.000 1.000   36.00 18.80 17.20 1.915
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.