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

Compare vibrational frequencies in CCCBDB for C4H4 (cyclobutadiene)

MP2/3-21G*

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Ag 3138 -2 Ag 3140 CH str
2 Ag 1448 -230 Ag 1678 C=C str
3 Ag 1068 9 Ag 1059 CH def
4 Ag 863 -126 Ag 989 CH def
5 Au 704        
6 Au 476        
7 B1g 787        
8 B1u 3122 -2 B1u 3124 CH str
9 B1u 1436 -91 B1u 1527 C=C str
10 B1u 1025 -3 B1u 1028 CH def
11 B2g 524 -7 B2g 531 CH OPLA
12 B2u 3102 -3 B2u 3105 CH str
13 B2u 1222 -22 B2u 1244 CH def
14 B2u 574 -145 B2u 719 ring def
15 B3g 3090 -3 B3g 3093 CH str
16 B3g 1161        
17 B3g 845        
18 B3u 564 -12 B3u 576 CH OPLA
The calculated vibrational frequencies were scaled by 0.9513

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.