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

Compare vibrational frequencies for two calculations for C4H4N2 (Pyrazine)

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 Ag Ag   3056 3060 -4.0 0.999   1.101 1.101 -0.000 1.000   0.00 0.00 0.00  
2 Ag Ag   1625 1547 78.0 1.050   4.879 4.674 0.204 1.044   0.00 0.00 0.00  
3 Ag Ag   1222 1208 14.9 1.012   1.236 1.225 0.011 1.009   0.00 0.00 0.00  
4 Ag Ag   1016 982 34.4 1.035   5.396 5.870 -0.474 0.919   0.00 0.00 0.00  
5 Ag Ag   588 571 16.9 1.030   8.757 8.814 -0.057 0.994   0.00 0.00 0.00  
6 Au Au   1009 905 103.4 1.114   1.510 1.539 -0.028 0.982   0.00 0.00 0.00  
7 Au Au   383 324 59.1 1.183   2.419 2.349 0.069 1.030   0.00 0.00 0.00  
8 B1g B1g   941 890 50.3 1.057   1.259 1.259 0.000 1.000   0.00 0.00 0.00  
9 B1u B1u   3035 3042 -7.4 0.998   1.091 1.091 0.000 1.000   10.13 5.66 4.47 1.788
10 B1u B1u   1502 1444 58.2 1.040   2.086 1.862 0.224 1.120   1.28 3.99 -2.72 0.320
11 B1u B1u   1134 1109 24.8 1.022   1.858 2.163 -0.305 0.859   8.36 3.15 5.21 2.652
12 B1u B1u   1007 980 26.4 1.027   6.114 5.508 0.607 1.110   40.86 37.88 2.98 1.079
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.