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

Compare vibrational frequencies in CCCBDB for C4H2 (Diacetylene)

B3LYP/CEP-121G

Frequency in cm-1
  Calculated   Experimental
Mode Number Symmetry Frequency diff Symmetry Frequency Comment
1 Σg 3366 73 Σg+ 3293  
2 Σg 2190 6 Σg+ 2184  
3 Σg 869 -5 Σg+ 874  
4 Σu 3366 37 Σu+ 3329  
5 Σu 1997 -23 Σu+ 2020  
6 Πg 1519 892 Πg 627  
7 Πg 725 243 Πg 482  
8 Πu 975 345 Πu 630  
9 Πu 326 95 Πu 231  
The calculated vibrational frequencies were scaled by 0.9745

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.