Theoretical Models of the Polar Cu2O(100) Cu+-Terminated Surface

Different reconstructions of the polar, cation-terminated (100) surface of Cu2O have been investigated. All surfaces have been fully relaxed employing a pair-potential and shell-model description of the interactions within the crystal. A (1 × 1) missing-row reconstruction gave the lowest surface energy, while the experimentally reported ( × )R45° surface structure could not be made stable. Quantum chemical models of the (1 × 1)-reconstructed surface were studied and the Cu+ (d10 → d9 s) excitation energy computed; relaxation of the surface leads to an increased excitation energy (1.89 eV) and a more ionic description compared with the reconstructed but unrelaxed surface (1.38 eV). The hydrogen atomic chemisorption energy was also computed; for the relaxed surface the computed binding energy of 2.06 eV is sufficiently below half the binding energy of H2 that hydrogen dissociation can be excluded. This is in agreement with experiment. For the unrelaxed surface the binding energy is higher, 2.26 eV, which would allow energetically for H2 to dissociate. The convergence of the Madelung potential for these nontrivial surfaces is investigated with the conclusion that it is favorable to perform the full Ewald summation. A program to compute the Gaussian integrals over the Madelung potential is reported.