2,209 research outputs found
Nanotubes and Peapods
No full textThe author report an updated review of the recent progress in the characterization of inorganic nanotubes and in the chemistry of tubular structures carried out by theoretical investigations, based on DFT methods, with particular emphasis devoted to the description of the novel hybrid nanopeapod structures
Noncovalent Complexes of the Noble‐Gas Atoms: Analyzing the Transition from Physical to Chemical Interactions
No full textThis is the pre-refereeing version of the following final paper " Stefano Borocci, Felice Grandinetti, Nico Sanna, Paola Antoniotti, Francesca Nunzi, Non-covalent complexes of the noble-gas atoms: analyzing the transition from physical to chemical interactions", published in Journal of Computational Chemistry, 2019, 40, 2318-2328.
https://doi.org/10.1002/jcc.2601
DFT Investigations of Formic Acid Adsorption on Single-Wall TiO<sub>2</sub> Nanotubes: Effect of the Surface Curvature
No full textWe carried out a theoretical study based on DFT calculations to provide a detailed characterization of the structural, electronic, and adsorption properties of single-walled TiO2 anatase nanotubes. We nanotube models of increasing diameter, formally obtained by rolling a TiO2 anatase monolayer around the [(1) over bar 01] and [010] directions, giving rise to (n,0) and (0,m) nanotubes, respectively. We considered finite cluster models for both (n,0) and (m,0) TiO2 nanotubes, with diameters ranging from 5 to 30 angstrom, thus' approaching realistic nanotube dimensions. Our results show that (n,0) tubes are lower in energy with respect to (0,m) tubes. For (n,0) tubes with diameters greater than 23 angstrom, the electronic energy and the band gap are almost converged with respect to the diameter length. We then investigated the adsorption of formic acid on the TiO2 nanotube sidewalls, as the simplest model of photosensitizers binding to the TiO2 surface, relevant to dye-sensitized solar cells. Adsorption of formic acid was investigated on (12,0) and (0,4) TiO2 nanotubes, optimizing two monodentate modes and one bidentate adsorption mode, and comparing the results to those obtained for a planar TiO2 surface. We find that while for a planar surface a bridged bidentate configuration is the more stable, the effect of the curvature in TiO2 nanotubes leads a monodentate configuration to be the more stable structure. These results are interpreted in terms of the peculiar electronic properties of TiO2 nanotubes and their implications for use of nanotubes in dye-sensitized solar cells are discussed
Ab Initio Simulation of the Absorption Spectra of Photoexcited Carriers in TiO2 Nanoparticles
No full textWe investigate the absorption spectra of photoexcited carriers in a prototypical anatase TiO2 nanoparticle using hybrid time dependent density functional theory calculations in water solution. Our results agree well with experimental transient absorption spectroscopy data and shed light on the character of the transitions. The trapped state is always involved, so that the SOMO/SUMO is the initial/final state for the photoexcited electron/hole absorption. For a trapped electron, final states in the low energy tail of the conduction band correspond to optical transitions in the IR, while final states at higher energy correspond to optical transitions in the visible. For a trapped hole, the absorption band is slightly blue-shifted and narrower in comparison to that of the electron, consistent with its deeper energy level in the band gap. Our calculations also show that electrons in shallow traps exhibit a broad absorption in the IR, resembling the feature attributed to conductive electrons in experimental 6 spectra
A Pyracylene Model for the Interaction of Transition Metal Complexes: A Density Functional Study
No full textA Density Functional Study on the Interaction of a Polycyclic Aromatic Molecule and the Silicon (001) Surface
No full textStatic and dynamical density functional theory calculations have been carried out to investigate the coordination and haptotropic rearrangement of the Cr(CO)(3) fragment on the (6,0) carbon nanotube sidewalls. Geometry optimizations have been performed on the Cr(CO)(3)-(C72H12) complex, pointing out the preferred coordination sites of the metal fragment on the nanotube sidewalls. We find a hole site configuration of the Cr(CO)(3) to be the global energy minimum of the Cr(CO)(3)-(C72H12) system, with a binding energy of 143 kJ mol(-1). The shifting of the Cr(CO)(3) complex between two coordination sites on adjacent hexagonal rings of (6,0) carbon nanotubes has been investigated by means of Car-Parrinello simulations, from which the transition state structure for the haptrotropic rearrangement has been localized and found to be 68 kJ mol(-1) above the global minimum structure
Selective functionalization of the Si(100) surface by a bi-functional alkynilamine molecule: a density functional study of the switching adsorption linkage
No full textThe reaction of the bifunctional organic molecule 1-dimethylamino-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations on a one-dimer cluster model. We found that, once in the physisorbed dative bonded well (-22.1 kcal mol(-1)), DMAP can proceed to react via a number of pathways. We first considered the cycloaddition of the C equivalent to C triple bond, leading to Si-C di-sigma bonded product (-58.6 kcal mol(-1)), computing an energy barrier of 33.1 kcal mol(-1). We considered also possible dissociative pathways of dative bonded DMAP, i.e., methylene C-H, methyl C-H or N-CH3 bond cleavage
Stabilization through p-dimethylaminobenzaldehyde of a new NLO-active phase of [E-4-(4-dimethylaminostyryl)-1-methylpyridinium] iodide: synthesis, structural characterization and theoretical investigation of its electronic properties
No full textCo-crystallization of p-N(CH3)2C6H4CHO and E-4-(4-dimethylaminostyryl)-1-methylpyridinium iodide ([DAMS]I) gives a new solid state form (A), characterized by high non-linear-optical (NLO) activity and quite different from the well known [DAMS]I salt (centrosymmetric and therefore inactive). The X-ray structural characterization, although affected by the extended disorder of p-N(CH3)2C6H4CHO, addresses a new kind of aggregation for the [DAMS+] chromophore molecules. In fact, together with the often encountered J-type aggregation, an unprecedented "fishbone" coupling is observed. Calculations using time-dependent density functional theory (TDDFT) prove that the absence of a J-aggregation band in the electronic absorption spectrum is due to the additional intermolecular interaction that quenches the expected J-type signal. Correlation between supramolecular arrangements of the chromophores and NLO properties is also discussed. © 2010 The Royal Society of Chemistry
Modelling Charge Transfer in Weak Chemical Bonds: Insights from the Chemistry of Helium
No full textWe studied the nature of the interaction of the weakly bound BeHe adduct by means of an integrated theoretical approach based on high-level quantum chemical calculations for the characterization of the potential energy surfaces and charge displaced upon adduct formation, together with the development of a semi-empirical analytical formulation of the interaction potential. Our results show that Be is able to form a stable adduct with He when the Be(1D) (1s2 2s2!1s2 2s0 2p2) excited state is involved, with a binding energy of as much as
10.2 kcal/mol, an astonishingly large value for He in neutral systems. The analysis of the leading interaction components in the Be*He adduct proves the relevance of the charge transfer to the overall stability, which contributes to decreasing the intermolecular distance, thus strengthening the induction-energy component
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