The adsorption profiles and electronic structures of Pt n ͑n =1-4͒ clusters on stoichiometric, reduced and reconstructed rutile TiO 2 ͑110͒ surfaces were systematically studied using on site d-d Coulomb interaction corrected hybrid density-functional-theory ͑DFT͒ calculations. The atomic structure of small Pt cluster adsorbates mainly depends on the stoichiometry of the corresponding titania support. The cluster shapes on the bulk terminated ideal surface look like their gas phase low-energy structures. However, for instance, they get significantly distorted on the reduced surfaces with increasing oxygen vacancies. On nonstoichiometric surfaces, Pt-Ti coordination becomes dominant in the determination of the adsorption geometries. The electronic structure of Pt n / TiO 2 ͑110͒ systems cannot be correctly described by pure DFT methods, particularly for nonstoichiometric cases due to the inappropriate treatment of the correlation for d electrons. We performed DFT+ U calculations to give a reasonable description of the reconstructed rutile ͑110͒ surface. Pt clusters induce local surface relaxations that influence band edges of titania support and bring a number of band-gap states depending on the cluster size. Significant band gap narrowing occurs upon Pt n -surface interaction due to adsorbate driven states on the bulk terminated and reduced surfaces. On the other hand, they give rise to a band-gap widening associated to partial reoxidation of the reconstructed surface. No metallization arises even for Pt 4 on rutile.

The structural profiles and electronic properties of pentacene (C 22 H 14 ) multilayers on Ag(111) surface has been studied within the density functional theory (DFT) framework. We have performed first-principle total energy calculations based on the projector augmented wave (PAW) method to investigate the initial growth patterns of pentacene (Pn) on Ag(111) surface.In its bulk phase, pentacene crystallizes with a triclinic symmetry while a thin film phase having an orthorhombic unit cell is energetically less favorable by 0.12 eV/cell. Pentacene prefers to stay planar on Ag(111) surface and aligns perfectly along silver rows without any molecular deformation at a height of 3.9 Å. At one monolayer (ML) coverage the separation between the molecular layer and the surface plane extends to 4.1 Å due to intermolecular interactions weakening surface-pentacene attraction. While the first ML remains flat, the molecules on a second full pentacene layer deposited on the surface rearrange so that they become skewed with respect to each other. This adsorption mode is energetically more preferable than the one for which the molecules form a flat pentacene layer by an energy difference similar to that obtained for bulk and thin film phases. Moreover, as new layers added, pentacenes assemble to maintain this tilting for 3 and 4 ML similar to its bulk phase while the contact layer always remains planar. Therefore, our calculations indicate bulk-like initial stages for the growth pattern.

No abstract

First-principles density functional calculations are performed within the local density approximation to study the electronic properties of SrZrO3, an insulating 4d-perovskite, in its high-temperature cubic phase, above 1400 K, as well as the generic 3d-perovskite SrTiO3, which is also a d 0 -insulator and cubic above 105 K, for comparison reasons. The energy bands, density of states and charge density distributions are obtained and a detailed comparison between their band structures is presented. The results are discussed also in terms of the existing data in the literature for both oxides.