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IV.C.1. (XIII.D.1.)

Compare vibrational frequencies in CCCBDB for C4H4 (cyclobutadiene)

BLYP/3-21G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Ag 3181 41 Ag 3140 CH str
2 Ag 1543 -135 Ag 1678 C=C str
3 Ag 1067 8 Ag 1059 CH def
4 Ag 881 -108 Ag 989 CH def
5 Au 866        
6 Au 532        
7 B1g 852        
8 B1u 3165 41 B1u 3124 CH str
9 B1u 1529 2 B1u 1527 C=C str
10 B1u 1034 6 B1u 1028 CH def
11 B2g 600 69 B2g 531 CH OPLA
12 B2u 3143 38 B2u 3105 CH str
13 B2u 1216 -28 B2u 1244 CH def
14 B2u 584 -135 B2u 719 ring def
15 B3g 3128 35 B3g 3093 CH str
16 B3g 1157        
17 B3g 859        
18 B3u 592 16 B3u 576 CH OPLA
The calculated vibrational frequencies were scaled by 0.9935

See section XIII.C.3 List or set vibrational scaling factors to change the scale factors used here.
See section III.B.3.c Calculate a vibrational scaling factor for a set of molecules to determine the least squares best scaling factor.
See section III.B.3.b List of vibrational scaling factors and their uncertainties for information on where the above scaling factor is from.