Inclusion of non-bonded interactions in calculations of vibrational frequencies

The consequences of including non-bonded interactions in the calculation of vibrational frequencies are examined by comparing the results of the consistent force field method (CFF)and a conventional spectroscopic force field calculation method. Sample calculations are given, using ethane as a test case. It is shown that the CFF method is more practical for the calculation of non-bonded interaction parameters for large molecules, provided that the molecular potential energy is first minimized.