arXiv subjects

Vincenzo Fiorentini

Publications and source records attributed to Vincenzo Fiorentini.

57 records · Page 4Linked to original sources

arXiv1993

Theory of Adsorption and Surfactant Effect of Sb on Ag (111)

We present first-principles studies of the adsorption of Sb and Ag on clean and Sb-covered Ag (111). For Sb, the {\it substitutional} adsorption site is found to be greatly favored with respect to on-surface fcc sites and to subsurface sites, so that a segregating surface alloy layer is formed. Adsorbed silver adatoms are more strongly bound on clean Ag(111) than on Sb-covered Ag. We propose that the experimentally reported surfactant effect of Sb is due to Sb adsorbates reducing the Ag adatom mobility. This gives rise to a high density of Ag islands which coalesce into regular layers.

cond-mat↗

arXiv1993

Reconstruction Mechanism of FCC Transition-Metal (001) Surfaces

The reconstruction mechanism of (001) fcc transition metal surfaces is investigated using a full-potential all-electron electronic structure method within density-functional theory. Total-energy supercell calculations confirm the experimental finding that a close-packed quasi-hexagonal overlayer reconstruction is possible for the late 5$d$-metals Ir, Pt, and Au, while it is disfavoured in the isovalent 4$d$ metals (Rh, Pd, Ag). The reconstructive behaviour is driven by the tensile surface stress of the unreconstructed surfaces; the stress is significantly larger in the 5$d$ metals than in 4$d$ ones, and only in the former case it overcomes the substrate resistance to the required geometric rearrangement. It is shown that the surface stress for these systems is due to $d$ charge depletion from the surface layer, and that the cause of the 4th-to-5th row stress difference is the importance of relativistic effects in the 5$d$ series.

cond-mat↗

arXiv1992

Electronic and structural properties of GaN by the full-potential LMTO method : the role of the $d$ electrons

The structural and electronic properties of cubic GaN are studied within the local density approximation by the full-potential linear muffin-tin orbitals method. The Ga $3d$ electrons are treated as band states, and no shape approximation is made to the potential and charge density. The influence of $d$ electrons on the band structure, charge density, and bonding properties is analyzed. It is found that due to the energy resonance of the Ga 3$d$ states with nitrogen 2$s$ states, the cation $d$ bands are not inert, and features unusual for a III-V compound are found in the lower part of the valence band and in the valence charge density and density of states. To clarify the influence of the Ga $d$ states on the cohesive properties, additional full and frozen--overlapped-core calculations were performed for GaN, cubic ZnS, GaAs, and Si. The results show, in addition to the known importance of non-linear core-valence exchange-correlation corrections, that an explicit description of closed-shell repulsion effects is necessary to obtain accurate results for GaN and similar systems. In summary, GaN appears to be somewhat exceptional among the III-V compounds and reminiscent of II-VI materials, in that its band structure and cohesive properties are sensitive to a proper treatment of the cation $d$ bands, as a result of the presence of the latter in the valence band range.

cond-mat↗