INTERACTION OF METHANE WITH A [LI](0) CENTER ON MGO(100) - HF, POST-HF, AND DFT CLUSTER MODEL STUDIES

We investigate the interaction between methane and a [Li](0) center on MgO(100) using ab initio cluster methodology. We focus on the catalyt ic activation of the C-H bond, an essential reaction step in the oxida tive coupling of methane (OCM), In the first part of the study we use a simple embedded cluster model that allows us to compare different le vels of theory and to study the influence of electron correlation on t he calculated energy profile for the H abstraction reaction. Hartree-F ock (HF) calculations are compared to results obtained from post-HF (M oller-Plesset perturbation theory) and gradient-corrected density func tional theory (DFT) computational schemes. We show that the use of the density functional exchange potential without self-interaction correc tions leads to sin inadequate potential energy surface for the hydroge n abstraction reaction at the [Li](0) center. The second part of the s tudy is devoted to Substrate relaxation effects, employing a much larg er cluster model The geometry of the lattice around the [Li](0) cener is optimized for key stages along the reaction path. Comparison with p revious studies shows the importance of including extensive relaxation if accurate geometries about the surface defect sites are to be calcu lated.