THEORETICAL-MODELS OF THE POLAR CU2O(100) CU-TERMINATED SURFACE()

Different reconstructions of the polar, cation-terminated (100) surfac e of Cu2O have been investigated. All surfaces have been fully relaxed employing a pair-potential and shell-model description of the interac tions within the crystal. A (1 x 1) missing-row reconstruction gave th e lowest surface energy, while the experimentally reported (3 root 2 x root 2)R45 degrees surface structure could not be made stable. Quantu m chemical models of the (1 x 1)-reconstructed surface were studied an d the Cu+ (d(10)-->d(9) s(1)) excitation energy computed; relaxation o f the surface leads to an increased excitation energy (1.89 eV) and a more ionic description compared with the reconstructed but unrelaxed s urface (1.38 eV). The hydrogen atomic chemisorption energy was also co mputed; for the relaxed surface the computed binding energy of 2.06 eV is sufficiently below half the binding energy of H-2 that hydrogen di ssociation can be excluded. This is in agreement with experiment. For the unrelaxed surface the binding energy is higher, 2.26 eV, which wou ld allow energetically for H-2 to dissociate. The convergence of the M adelung potential for these nontrivial surfaces is investigated with t he conclusion that it is favorable to perform the full Ewald summation . A program to compute the Gaussian integrals over the Madelung potent ial is reported.