METHYL ADDITION TO ACETYLENE AND ETHYLENE FROM A DENSITY-FUNCTIONAL APPROACH

The addition of methyl radical to ethylene and acetylene has been stud ied by different density functionals and basis sets. The results show that only inclusion of some Hartree-Fock exchange in a particular grad ient-corrected functional (B3LYP model) leads to reliable results for geometries, reaction and activation energies. Although quite large bas is sets are apparently needed to obtain converged results, explicit co nsideration of the basis set superposition error significantly improve s the results provided by medium size basis sets. The results are furt her interpreted in terms of the deformation energy of the fragments an d of a partitioning of their interaction energy on the basis of the so -called natural bond orbitals.