Static simulation of bulk and selected surfaces of anatase TiO2

A theoretical investigation has been carried out to characterize bulk and selected surfaces of anatase TiO2. The calculations are performed using a B3LYP hybrid functional and 6-31G basis set within the periodic density functional approximation. Optimization procedures have been employed to determine the equilibrium geometry of the crystal and slab surface models. The compressibility, band structure, and the bulk and surface charge distributions are reported. The surface relative energies are identified to follow the sequence: (001) < (101) < (100) much less than (110) < < < (111), from the most stable surface to the least stable one. Relaxation of (001) and (101) surfaces are moderate, with no displacements exceeding; approximate to0.19 Angstrom. The theoretical results are compared with previous theoretical studies and available experimental data. (C) 2001 Elsevier B.V. B.V. All rights reserved

Theoretical analysis of the energy levels induced by oxygen vacancies and the doping process (Co, Cu and Zn) on SnO2 (110) surface models

Density functional calculation at B3LYP level was employed to study the surface oxygen vacancies and the doping process of Co, Cu and Zn on SnO2 (110) surface models. Large clusters, based on (SnO2)(15) models, were selected to simulate the oxidized (Sn15O30), half-reduced (Sn15O29) and the reduced (Sn15O28) surfaces. The doping process was considered on the reduced surfaces: Sn13Co2O28, Sn13Cu2O28 and Sn13Zn2O28. The results are analyzed and discussed based on a calculation of the energy levels along the bulk band gap region, determined by a projection of the monoelectron level structure on to the atomic basis set and by the density of states. This procedure enables one to distinguish the states coming from the bulk, the oxygen vacancies and the doping process, on passing from an oxidized to a reduced surface, missing bridge oxygen atoms generate electronic levels along the band gap region, associated with 5s/5p of four-/five-fold Sn and 2p of in-plane O centers located on the exposed surface, which is in agreement with previous theoretical and experimental investigations. The formation energy of one and two oxygen vacancies is 3.0 and 3.9 eV, respectively. (C) 2001 Elsevier B.V. B.V. All rights reserved

The Nature Of The Chemical Bond In Di- And Polynuclear Metal Cluster Complexes As Depicted By The Analysis Of The Electron Localization Function

The bonding in transition metal complexes is usually rationalized based on molecular orbital schemes. Topological approaches such as the atoms in molecules (AIM) theory or the electron localization function (ELF) analysis provides an alternative interpretation of the bonding relying on a local description. These topological theories give a very convenient framework to achieve the partition of the molecular space in regions with chemical meaning such as atoms, bonds and lone pairs. In this work we review the possibility offered by ELF to investigate the bond in di- tri- and tetranuclear metal complexes containing metal-metal bond. In the case of bimetallic complexes with different nominal bond orders of formula M2(formamidinate)4, the metal-metal interaction is associated to a large electron fluctuation between the two metallic cores and interpreted in terms of simple resonance arguments. Such fluctuation between metals can not be invoked for the trinuclear Fe3(CO)12 or the incomplete cuboidal [Mo3S4(PH3)6 Cl3]4+ complexes. The metal-metal interaction in these clusters is mostly characterized by multicenter bonding as is the case for the tetranuclear heterodimetallic cubane-type complexes resulting from the insertion of Cu or Ni into the previous Mo3 S4 complex. © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved.89-10 SPEC. ISS.14001412Cotton, F.A., (1993) Multiple Bonds Between Metal Atoms, , Oxford, UK: Oxford University Press. second edCotton, F.A., Nocera, D.G., (2000) Acc. Chem. Res., 33, p. 483Gagliardi, L., Roos, B.O., (2003) Inorg. Chem., 42, pp. 1599-1603Bradley, P.M., Smith, L.T., Eglin, J.L., Turro, C., (2003) Inorg. Chem., 42, p. 7360Bader, R.F.W., (1990) A Quantum Theory Atoms in Molecules, , Oxford, UK: Oxford University PressSilvi, B., Savin, A., (1994) Nature, 371, p. 683Fradera, X., Austen, M.A., Bader, R.F.W., (1998) J. Phys. Chem. A, 103, p. 304Cremer, D., Kraka, E., (1984) Angew. Chem. Int. Ed. Engl., 23, p. 67Lewis, G.N., (1919) J. Am. Chem. Soc., 38, p. 762Lewis, G.N., (1966) Valence and the Structure of Atoms and Molecules, , New York: DoverGillespie, R.J., (1972) Molecular Geometry, , London: Van Nostrang ReinholdAslangul, C., Constanciel, R., Daudel, R., Kottis, P., (1972) Aspects of the Localizability of Electrons and Molecules: Loge Theory and Related Methods, , New York: Academic PressDaudel, R., (1971) Aspects De La Chimie Quantique Contemporaine, , Paris: Éd. CNRSBecke, A.D., Edgecombe, K.E., (1990) J. Phys. Chem., 92, p. 5397Silvi, B., (2004) Phys. Chem. Chem. Phys., 6, p. 256Silvi, B., (2003) J. Phys. Chem. A, 107, p. 3081Savin, A., Silvi, B., Colonna, F., (1996) Can. J. Chem., 74, p. 1088Cotton, F.A., (1965) Inorg. Chem., 4, p. 334Cotton, F.A., Feng, X., (1997) J. Am. Chem. Soc., 119, p. 7514Llusar, R., Beltrán, A., Andrés, J., Fuster, F., Silvi, B., (2001) J. Phys. Chem. A, 105, p. 9460Wang, S.G., Schwarz, W.H.E., (1998) J. Chem. Phys., 109, p. 7252Savin, A., Nesper, R., Wengert, S., Fässler, T., (1997) Angew. Chem. Int. Ed. Engl., 36, p. 1808Bianchi, R., Gervasio, G., Marabello, D., (2000) Inorg. Chem., 39, p. 2360Macchi, P., Proserpio, D.M., Sironi, A., (1998) J. Am. Chem. Soc., 120, p. 13429Bianchi, R., Gervasio, G., Marabello, D., (1998) Chem. Commun., 15, p. 1535Llusar, R., Beltrán, A., Andrés, J., Noury, S., Silvi, S., (1999) J. Comput. Chem., 20, p. 1517Silvi, B., Gatti, C., (2000) J. Phys. Chem. A, 104, p. 947Wei, C.H., Dahl, L.F., (1969) J. Am. Chem. Soc., 91, p. 1351Cotton, F.A., Troup, J.M., (1974) J. Am. Chem. Soc., 96, p. 4155Chevreau, H., Martinsky, C., Sevin, A., Minot, C., Silvi, B., (2003) New J. Chem., 27, p. 1049Hunstock, E., Mealli, C., Calhorda, M.J., Reinhold, J., (1999) Inorg. Chem., 38, p. 5053Pilme, J., Silvi, B., Alikhani, M.E., (2003) J. Phys. Chem. A, 107, p. 4506Dewar, M.J.S., (1951) Bull. Soc. Chim., 18Chatt, J., Duncanson, L.A., (1953) J. Am. Chem. Soc., p. 2939Müller, A., Jostes, R., Cotton, F.A., (1980) Angew. Chem. Int. Ed. Engl., 19, p. 875Cotton, F.A., Llusar, R., (1987) Polyhedron, 6, p. 1741Feliz, M., Llusar, R., Andres, J., Berski, S., Silvi, B., (2002) New J. Chem., 26, p. 844Cotton, F.A., Haas, T.E., (1964) Inorg. Chem., 3, p. 10Cotton, F.A., Haas, T.E., (1964) Inorg. Chem., 3, p. 1217Vergamini, P.J., Vahrenkamp, H., Dahl, L.F., (1971) J. Am. Chem. Soc., 93, p. 6327Bursten, B.E., Cotton, F.A., Hall, M.B., Najjar, R.C., (1982) Inorg. Chem., 21, p. 302Jiang, Y., Tang, A., Hoffmann, R., Huang, J., Lu, J., (1985) Organometallics, 4, p. 27Li, J., Liu, C., Lu, J., (1994) Polyhedron, 13, p. 1841Feliz, M., Garriga, J.M., Llusar, R., Uriel, S., Humphrey, M.G., Lucas, N.T., Samoc, M., Luther-Davies, B., (2001) Inorg. Chem., 40, p. 6132Feliz, M., (2003), PhD thesis, Universitat Jaume I, Castelló, SpainBahn, C.S., Tan, A., Harris, S., (1998) Inorg. Chem., 37, p. 2770Llusar, R., Uriel, S., (2003) Eur. J. Inorg. Chem., 7, p. 1271Akashi, H., Uryu, N., Shibahara, T., (1997) Inorg. Chim. Acta, 261, p. 5

Periodic study on the structural and electronic properties of bulk, oxidized and reduced SnO2(110) surfaces and the interaction with O-2

The structural and electronic properties of bulk and both oxidized and reduced SnO2(110) surfaces as well as the adsorption process of O-2 on the reduced surface have been investigated by periodic DFT calculations at B3LYP level. The lattice parameters, charge distribution, density of states and band structure are reported for the bulk and surfaces. Surface relaxation effects have been explicitly taken into account by optimizing slab models of nine and seven atomic layers representing the oxidized and reduced surfaces, respectively. The conductivity behavior of the reduced SnO2(110) surface is explained by a distribution of the electrons in the electronic states in the band gap induced by oxygen vacancies. Three types of adsorption approaches of O-2 on the four-fold tin at the reduced SuO(2)(110) surface have been considered. The most exothermic channel corresponds to the adsorption of O-2 parallel to the surface and to the four-fold tin row, and it is believed to be associated with the formation of a peroxo O-2(2-) species. The chemisorption of O-2 on reduced SnO2(110) surface causes a significant depopulation of states along the band gap and it is shown to trap the electrons in the chemisorbed complex producing an electron-depleted space-charge layer in the inner surface region of the material in agreement with some experimental evidences. (C) 2002 Elsevier B.V. B.V. All rights reserved

Oxygen Atom Transfer Reactions from Mimoun Complexes to Sulfides and Sulfoxides. A Bonding Evolution Theory Analysis

In this research, a comprehensive theoretical investigation has been conducted on oxygen atom transfer (OAT) reactions from Mimoun complexes to sulfides and sulfoxides. the joint use of the electron localization function (ELF) and Thom's catastrophe theory (CT) provides a powerful tool to analyze the evolution of chemical events along a reaction pathway. the progress of the reaction has been monitored by structural stability domains from ELF topology while the changes between them are controlled by turning points derived from CT which reveal that the reaction mechanism can be separated in several steps: first, a rupture of the peroxo O-1-O-2 bond, then a rearrangement of lone pairs of the sulfur atom occurs and subsequently the formation of S-O-1 bond. the OAT process involving the oxidation of sulfides and sulfoxides is found to be an asynchronous process where O-1-O-2 bond breaking and S-O-1 bond formation processes do not occur simultaneously. Nudeophilic/electrophilic characters of both dimethyl sulfide and dimethyl sulfoxide, respectively, are sufficiently described by our results, which hold the key to unprecedented insight into the mapping of electrons that compose the bonds while the bonds change.Generalitat ValencianaSpanish Ministry Ministerio de Economiay CompetitividadSpanish-Brazilian programFundacion Bancaixa-Universitat Jaume I (UJI)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)São Paulo State Univ, Inst Chem, Interdisciplinary Lab Electrochem & Ceram, BR-14800900 Araraquara, BrazilUniv Jaume 1, Dept Quim Fis & Analit, Castellon de La Plana 12071, SpainUniversidade Federal de São Paulo, UNIFESP, Dept Ciencias Exatas & Terra, BR-09913030 Diadema, BrazilUniv Fed Sao Carlos, Dept Chem, Interdisciplinary Lab Electrochem & Ceram, BR-13565905 Sao Carlos, SP, BrazilUniversidade Federal de São Paulo, UNIFESP, Dept Ciencias Exatas & Terra, BR-09913030 Diadema, BrazilGeneralitat Valenciana: Prometeo/2009/053Spanish Ministry Ministerio de Economiay Competitividad: CTQ-2012-36253-C03-01Spanish-Brazilian program: PHB2009-0065-PCFundacion Bancaixa-Universitat Jaume I (UJI): P1.1B2010-10FAPESP: 2009/01628-8Web of Scienc

Recent research developments in SnO2-based varistors

This paper discusses some advances in research conducted on SnO2-based electroceramics. The addition of different dopants, as well as several thermal treatments in oxidizing and inert atmospheres, were found to influence the microstructure and electrical properties of SnO2-based varistor ceramics. Measurements taken by impedance spectroscopy revealed variations in the height and width of the potential barrier resulting from the atmosphere in which thermal treatments were performed. High nonlinear coefficient values, which are characteristic of high-voltage and commercial ZnO varistors, were obtained for these SnO2-based systems. All the systems developed here have potentially promising varistor applications. (C) 2004 Elsevier B.V. All rights reserved

The origin of photoluminescence in amorphous lead titanate

We discuss the nature of visible photoluminescence at room temperature in amorphous lead titanate in the light of the results of recent experimental and theoretical calculations. Experimental results obtained by XANES and EXAFS revealed that amorphous lead titanate is composed of a Ti-O network having fivefold Ti coordination and NBO-type (non-bridging oxygen) defects. These defects can modify the electronic structure of amorphous compounds. Our calculation of the electronic structure involved the use of first-principle molecular calculations to simulate the variation of the electronic structure in the lead titanate crystalline phase, which is known to have a direct band gap, and we also made an in-depth examination of amorphous lead titanate. The results of our theoretical calculations of amorphous lead titanate indicate that the formation of fivefold coordination in the amorphous system may introduce delocalized electronic levels in the HOMO ( highest occupied molecular orbital) and the LUMO ( lowest unoccupied molecular orbital). A comparison of the experimental and theoretical results of amorphous compounds suggests the possibility of a radiative recombination (electron-hole pairs), which may be responsible for the emission of photoluminescence. (C) 2003 Kluwer Academic Publishers