Density functional based studies of transition states and barriers for hydrogen exchange and abstraction reactions

The overbinding that is inherent in existing local approximations to the density functional formalism has limited the usefulness of the local density approximation (LDA) for describing phenomena that are mediated by reaction barriers. Since the generalized gradient approximation (GGA) significantly decreases the overbinding, prospects for density functional based reaction dynamics are promising. Using both LDA and GGA functionals, we determined the transition state properties for four different reactions; H2+H→H+H2, CH4+H→CH3+H2,H+CH4→CH4 +H, and CH4+CH3 →CH3+CH4. Although we find that GGA still underestimates reaction barriers, our results show that this functional leads to significant improvements of the calculated reaction barriers and energetics.