ELECTRONIC-STRUCTURE CALCULATIONS OF HYDROCARBON RADICAL CATIONS - A DENSITY-FUNCTIONAL STUDY

The radical cations of methane, ethane, propane, n-butane, ethene, propene, and 1- and 2-butene are optimized at the first principles LCGTO-DFT level, using a DZP basis set and including nonlocal corrections to the exchange and correlation functionals. The optimized geometries are reported and compared with previously reported structures, obtained at the ab initio UHF or MP2 levels. The calculations show a general agreement between the DFT and MP2 optimized structures, although the DFT results tend to overestimate the C-H bond lengths by 0.02 angstrom. The structures of the carbon frameworks and all bond angles are, however, in very good agreement between the two methods. One notable exception is observed for the ethane cation, where the DFT calculations predict a much shorter bond length for the ionized C-C sigma-bond (1.49 angstrom vs 1.58 angstrom (MP2/6-31G**)).