STUDY OF SOME ORGANIC-REACTIONS USING DENSITY-FUNCTIONAL THEORY

Twelve organic reactions (six closed shell and six radical) were studied using semiempirical, traditional ab initio and density functional methodologies. Full geometry optimizations of all species, both minima and transition states, were performed, and calculated geometries and barrier heights compared with experimental data. Our results demonstrate that although currently available density functionals tend to underestimate barrier heights, especially for radical reactions-in some cases reactions with low barriers are predicted to be essentially barrier free-they provide a significant improvement over standard methods. The adiabatic connection method recently proposed by Becke [J. Chem. Phys. 98, 5648 (1993)], in which a portion of the exact Hartree-Fock exchange is mixed in to the density functional, looks very promising. © 1994 American Institute of Physics.