A STUDY OF THE ENERGETICS OF THE CL2 MGO(001) INTERFACE USING CORRELATION CORRECTED PERIODIC HARTREE-FOCK THEORY/

The energetics of the Cl2/MgO(001) interface were investigated using t he ab initio periodic Hartree-Fock (PHF) method and local density func tional correlation corrections to PHF theory, as implemented in the pr ogram CRYSTAL92. Estimates of the correlation corrected PHF energies a re made by post-SCF evaluations of three gradient corrected functional s. The correlation energy is calculated from the fully converged groun d state PHF charge density and added to the PHF total energy. This is the first study of interfacial energetics using the correlation correc ted PHF theory. PHF and correlation corrected molecule/surface binding energies are reported for seven orientations of the adsorbate with re spect to the surface plane. Three of the configurations align the intr amolecular axes along the surface normal and the remaining geometries arrange the molecules heat-to-tail, parallel to the surface plane. The most favorable interaction occurs when chlorine approaches a surface oxygen along the normal direction. This site preference is consistent with a classical electrostatic description of the physisorption proces s. The binding energy increases with decreasing surface coverage. At t he most dilute coverage studied (1:8) the PHF binding energy was 4.1 k cal/mol and the correlation corrected binding energies ranged from 9.2 to 10.3 kcal/mol. All three functionals tended to increase the molecu le/surface attractions, shorten the molecule/surface equilibrium dista nce, increase the curvature of the molecule/surface potential energy s urface near equilibrium, and reduce the molecule/molecule repulsions.