Search results for "Density Functional Theory."
showing 10 items of 935 documents
The electronic structure of zircon-type orthovanadates: Effects of high-pressure and cation substitution
2012
The electronic structure of four ternary-metal oxides containing isolated vanadate ions is studied. Zircon-type YVO4, YbVO4, LuVO4, and NdVO4 are investigated by high-pressure optical-absorption measurements up to 20 GPa. First-principles calculations based on density-functional theory were also performed to analyze the electronic band structure as a function of pressure. The electronic structure near the Fermi level originates largely from molecular orbitals of the vanadate ion, but cation substitution influence these electronic states. The studied ortovanadates, with the exception of NdVO4, undergo a zircon-scheelite structural phase transition that causes a collapse of the band-gap energ…
Factors Controlling the Energy of Nitrogen Monolayer Coverage onHigh Surface Area Catalyst Oxide Carriers
2011
Factors affecting the strength of nitrogen physisorption at monolayer coverage on different catalytic oxide carriers (e.g., ZnO, MgO, Al2O3, ZrO2, TiO2, and SiO2) have been addressed. Isotherm elaboration by the two-parameter BET equation provides C-constant values (80–200) inversely related to the polarizing power (PP) of the oxide adsorbent irrespective of the surface area exposure. The energy of monolayer formation depends on the extent of charge-delocalization characterizing the surface cation-oxygen bond, which determines the acid–base character of the oxide and strength of van der Waals interactions with adsorbate molecules. Density functional theory (DFT) calculations on MgO and TiO2…
Copper(i) complexes for sustainable light-emitting electrochemical cells
2011
Four prototype heteroleptic copper(I) complexes [Cu(bpy)(pop)][PF6] (bpy = 2,2′-bipyridine, pop = bis(2-(diphenylphosphino)phenyl)ether), [Cu(phen)(pop)][PF6] (phen = 1,10-phenanthroline), [Cu(bpy)(pdpb)][PF6] (pdpb = 1,2-bis(diphenylphosphino)benzene) and [Cu(phen)(pdpb)][PF6] are presented. The synthesis, X-ray structures, solution and solid-state photophysical studies, and the performance in light-emitting electrochemical cells (LECs) of these complexes are described. Their photophysical properties are interpreted with the help of density functional theory (DFT) calculations. The photophysical studies in solution and in the solid-state indicate that these copper(I) complexes show good lu…
Growth, single crystal investigation, hirshfeld surface analysis, DFT studies, molecular docking, physico-chemical characterization and, in vitro, an…
2021
Abstract Interaction of the diphosphoric acid (H4P2O7) and organic ligand (3.4-dimethylaniline) with transition metal ions, cobalt (II) chloride leads to the formation of novel stable Co(II)-diphosphate cluster with empirical formula (C8H12N)2[Co(H2P2O7)2(H2O)2].2H2O. The structure of the synthesized material was confirmed by single crystal XRD at 120 K. The crystal was plate and crystallized in the triclinic P 1 ¯ space group with a = 7.5340(4) A, b = 7.5445(4) A, c = 13.6896(8) A, α = 84.215(5)°, β = 76.038(5)°, γ = 74.284(5)°, V = 726.38(7) A3 and Z = 1. Full-matrix least-squares refinement converged at R = 0.035 and Rw = 0.088 for 3636 independent observed reflectio…
Archetype Cationic Iridium Complexes and Their Use in Solid-State Light-Emitting Electrochemical Cells
2009
The archetype ionic transition-metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline, are used as the primary active components in light-emitting electrochemical cells (LECs). Solution and solid-state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn-on times (70 and 160 h, respectively) and low external quantum efficiencies (~ 2%) when the complex is used as a pure film. The long turn-on times are attributed to the low mobility of the counter…
Nanophase Segregation of Self-Assembled Monolayers on Gold Nanoparticles
2017
International audience; Nanophase segregation of a bi-component thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of inter-chain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by trans…
Hard sphere fluids at a soft repulsive wall: A comparative study using Monte Carlo and density functional methods
2011
Hard-sphere fluids confined between parallel plates at a distance D apart are studied for a wide range of packing fractions including also the onset of crystallization, applying Monte Carlo simulation techniques and density functional theory. The walls repel the hard spheres (of diameter σ) with a Weeks-Chandler-Andersen (WCA) potential V(WCA)(z) = 4ε[(σ(w)/z)(12) - (σ(w)/z)(6) + 1/4], with range σ(w) = σ/2. We vary the strength ε over a wide range and the case of simple hard walls is also treated for comparison. By the variation of ε one can change both the surface excess packing fraction and the wall-fluid (γ(wf)) and wall-crystal (γ(wc)) surface free energies. Several different methods t…
Spectroscopic characterization of non-covalent CuPc-GO system. Experiment and theory
2019
Abstract In this study we report on UV-vis, IR and Raman studies of non-covalent copper phthalocyanine (CuPc) – flake graphene oxide (GO) complex in water and in the solid phase. Experimental results were supported by molecular modeling of structure, electronic and vibrational parameters for free CuPc and its 1 : 1 complexes with water, benzene, phenol, neutral and deprotonated benzoic acid. HOMO-LUMO gaps for these complexes were calculated and compared with data derived from the absorption edge of Q-band in the recorded UV-vis spectra for free CuPc and its adduct with GO in water. Small but non-negligible changes in position of spectral bands observed as result of CuPc interaction with GO…
Two-Dimensional Antimony Oxide
2020
Two-dimensional (2D) antimony, so-called antimonene, can form antimonene oxide when exposed to air. We present different types of single- and few-layer antimony oxide structures, based on density functional theory (DFT) calculations. Depending on stoichiometry and bonding type, these novel 2D layers have different structural stability and electronic properties, ranging from topological insulators to semiconductors with direct and indirect band gaps between 2.0 and 4.9 eV. We discuss their vibrational properties and Raman spectra for experimental identification of the predicted structures.
Adsorbate-Induced Oxygen Vacancy Mobility in Ultrathin Oxide Films
2013
Oxides at the nanometric scale show a behavior markedly different from that of their bulk counterparts. Ultrathin oxides grown on metals do not reach the full insulator regime, and they cannot decouple the electronic clouds of incoming adsorbates from that of the metal substrate. Although oxygen vacancies control the chemical and physical properties of ultrathin oxide films, the role of intrinsic defects has been overlooked so far. By means of density functional theory methods, we show that the addition of atoms with high electron affinity, such as Au, to ultrathin MgO grown either on a Ag or Mo support, completely reverses the preferential positions of oxygen vacancies, decreases their res…