The influence of homoatomic d10···d10 interactions in the structural and physical properties of some copper-containing oxides has been investigated by using semiempirical band structure calculations of the extended Hückel type. Comparison of the band structures of CuAlO2 and Cu2O, two compounds with Cu(I) ions in practically identical coordination environments, reveals that the spatial arrangement of Cu···Cu contacts is responsible for their markedly different electrical and optical properties. The three-dimensional net of short Cu···Cu distances present in Cu2O is found to be essential for the appearance of color in this p-type semiconductor. In doped CuAlO2, on the contrary, the 2-D nature of the array of Cu···Cu contacts leads to optical transparency and a lower conductivity if compared to cuprite.

The structural and electronic properties of some simple ternary oxides with the delafossite-type structure have been investigated using the periodic Hartree-Fock method and a posteriori density-functional corrections. The coexistence in the same crystal structure of different structural motifs, such as MO 6 octahedra, linear O-Cu-O units, and hexagonal Cu layers with relatively short Cu-Cu distances, enables accurate calculation of the structural data for this type of material rather difficult: correlation effects seem only to be important for the description of the Cu-O bonds, while the geometry of the MO 6 octahedra is best described by the Hartree-Fock method. The analysis of bonding in the Cu layers reveals the existence of weak d 10 -d 10 interactions that are suggested to be important in the determination of the electrooptical properties of doped delafossites.

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