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

Different reconstructions of the polar, cation-terminated (100) surface of Cu 2 O 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 ( × ) R 45° surface structure could not be made stable. Quantum chemical models of the (1 × 1)-reconstructed surface were studied and the Cu + (d 10 → d 9 s 1 ) 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 H 2 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 H 2 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.