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Imines obtained by condensation of 4-hydroxybenzohydrazide with aliphatic ketones are a rare example of a class of compounds showing a remarkable tendency to crystallize in acentric polar space groups (Pna21 or Cc). In fact, all of the (seven) compounds studied up to now show at least one polar polymorph. In some cases, polymorphism was detected, and a nonpolar centrosymmetric phase was also identified (P21/c or P21/n space group). With the aim to disclose the conditions that can favor the formation of acentric structures in molecular crystals, we report, in this paper, a theoretical analysis (ab initio density functional theory with periodic boundary) of the lattice energy and density of all the packing modes observed in the whole set of imines. The computational analysis has been performed by optimizing each compound in its own experimental packings (actual crystal structures) and also in the packings of the other compounds of the class (virtual structures). The experimental crystallographic data and the theoretical analysis suggest that two conformers, basically differing for the orientation of the phenolic H atom in the plane of the phenyl ring, compete, in solution, for the formation of polar or centrosymmetric packings. The transitions between polar and centrosymmetric polymorphs are of diffusive type, and single crystals are not preserved, while the transitions between different polar polymorphs can be of single-crystal-to-single-crystal type.

Series of ZnII complexes with coordinated pyridine and a O,N,O tridentate core are reported. Four species of the general formula ZnLiPy2 were synthesized, where Li is a substituted ((aroylhydrazono)methyl)-3-hydroxyphenyl-4-(octyloxy)benzoate. The structure of the four mononuclear complexes and of dinuclear Zn2L24Py2 was solved by single crystals X-ray analysis. By TGA-DSC analysis and optical observation a nematogenic phase behavior was detected for ligands only and not for complexes. Photoluminescence spectra were recorded both in solution and in solid state Only the complexes showed a noteworthy photoluminescence in the solid state with tunable wavelength by varying the aroyl group. Medium to very high PL quantum yields were recorded on the crystalline complexes obtained in their mononuclear coordination environment. In the case of 4-nitrobenzoyl substituent a dinuclear complex with formula Zn2L24Py2 showed an unprecedent exceptionally high PLQY value. Both periodic and molecular DFT calculations were performed to rationalize the absorbance of these complexes at “one particle” level.

cited By 0; International audience; The VN3H defect in diamond (a vacancy surrounded by three nitrogen and one carbon atoms, the latter being saturated by a hydrogen atom) is investigated quantum-mechanically by use of a periodic supercell approach, an all-electron Gaussian-type basis set, "hybrid" functionals of density functional theory, and the Crystal program. Three fully optimized structural models (supercells containing 32, 64, and 128 atoms) are considered to investigate the effect of defect concentration. The electronic configuration of the defect is reported along with a description of its structural features. In particular, the influence of the lone-pair electrons of the three nitrogen atoms on the C-H bond is discussed. A thorough characterization of the vibrational spectroscopic features of the VN3H defect is also presented, where the anharmonicity of the most relevant normal modes is discussed. The infrared and Raman spectra show specific peaks, which allow for the identification of this particular defect among the many defects that are commonly present in both natural and irradiation-damaged diamonds. In particular, the main feature of the spectral fingerprint of the defect (i.e. the C-H stretching mode), experimentally observed at 3107 cm-1, is here computed at 3094 cm-1 with the B3LYP "hybrid" functional (with an anharmonic redshift of 157 cm-1 with respect to its harmonic value). The role played by the three nitrogen atoms on the spectral features of the defect is clearly identified through the redshift due to the 14N → 15N isotopic substitution. © 2017 the Owner Societies.

The adsorption of TiCl4 on the surfaces of MgCl2 crystals has been investigated by means of state-of-the-art periodic hybrid DFT methods, as the first step of a comprehensive study aiming to elucidate the structure of the active species in industrial MgCl2-supported Ziegler-Natta catalysts for ethene and propene polymerization. A first distinctive feature of the approach was the thorough evaluation of dispersion forces, crucial because the binding of TiCl4 on MgCl2 surfaces turned out to be essentially dispersion-driven. Also important was a careful investigation of the effects of different choices on basis set and density functional (DF) on the quantitative aspects of the results; this allowed us to trace the unusually large disagreement in the previous literature and identify unambiguous trends. In particular, three full sets of calculations were run adopting the B3LYP(-D), PBE0(-D) and M06 approximations: to the best of our knowledge, the last represents the first case of M06 functional implementation in a periodic code (CRYSTAL) of widespread use. The results consistently indicated that the adsorption of TiCl4 on well-formed MgCl2 crystals under conditions relevant for catalysis can only occur on MgCl2(1 1 0) or equivalent lateral faces, whereas the interaction with MgCl2(1 0 4) - for decades claimed as the most important surface in stereoselective catalysts - is too weak for the formation of stable adducts. The implications of these findings for catalysis are discussed. (C) 2011 Elsevier Inc. All rights reserved.

The relative stability of nine different well defined CeO2 surfaces has been studied by periodic density functional calculations using GGA + U and B3LYP exchange-correlation functional. Both methods consistently predict that CeO2(111) is the most stable surface and also provide a consistent picture of the most stable surfaces which indeed are in agreement with previous studies based on empirical interatomic potentials. The facility of ceria surfaces to undergo a redox process has been investigated by forcing spin-polarized solutions, which lead to the occupancy of Ce 4f orbitals. These calculations provide evidence that surfaces with low-coordinated Ce cations are likely to be reduced more easily than regular low-index Miller surfaces. Fil: Branda, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina Fil: Ferullo, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina Fil: Causá, Mauro. Università degli Studi di Napoli Federico II; Italia Fil: Illas, Francesc. Universidad de Barcelona; España

Graphite, and particularly defective graphite, is chosen to model soot particles. Quantum mechanical calculations are first carried out on molecular polycyclic-aromatic-hydrocarbon-type systems and then extended to a periodic representation of one graphite layer. The features of the interaction of H, HO, NO, NO2, and NO3 with these model systems are examined, with the aim of defining a suitable representation of the atmospheric or combustion gas−solid interactions by which functionalization reactions can take place. The more interesting interactions with small reactive molecules regard the edge of the graphene sheet and the in-plane carbon vacancies. While these interactions can be well described by sufficiently extended molecular models, periodic models are necessary to describe accurately the equilibrium geometries because they introduce the necessary geometric constraints. The ability of a graphene sheet to easily accommodate unpaired electrons in σ or π orbitals is the basis for its interesting intera...

5 pags.; 2 figs.; 2 tabs., In this work we propose a general strategy to calculate accurate He-surface interaction potentials. It extends the dispersionless density functional (dlDF) approach recently developed by Pernal et al. [Phys. Rev. Lett. 109, 263201 (2009)] to adsorbate-surface interactions by including periodic boundary conditions. We also introduce a scheme to parametrize the dispersion interaction by calculating two- and three-body dispersion terms at CCSD(T) level via the method of increments [Stoll, J. Chem. Phys. 97, 8449 (1992)]. The performance of the composite approach is tested on 4He/graphene by determining the energies of the low-lying selective adsorption states, finding an excellent agreement with the best available theoretical data. Second, the capability of the approach to describe dispersionless correlation effects realistically is used to extract dispersion effects in time-dependent density functional simulations on the collision of 4He droplets with a single graphene sheet. It is found that dispersion effects play a key role in the fast spreading of the 4He nanodroplet, the evaporation-like process of helium atoms, and the formation of solid-like helium structures. These characteristics are expected to be quite general and highly relevant to explain experimental measurements with the newly developed helium droplet mediated deposition technique. © 2014 AIP Publishing LLC, This work has been supported by Grants Nos. CCG08-CSIC/ESP-3680 from CSIC-CM, FIS2011-29596-C02-01 and FIS2011-28617- C02-01 from DGI, Spain (FEDER), and 2009SGR1289 from Generatitat de Catalunya.

The role of surface oxygen vacancies in the optical properties of tin dioxide nanobelts is investigated in this paper. Using a first-principles approach, based on the density functional theory combined to a very accurate exchange correlation functional, we characterize SnO(2) (101), that is the nanobelt largest surface. We show that the presence of surface oxygen vacancies leads to the appearance of (i) occupied states located at about 1 eV above the valence band and (ii) unoccupied states lying in resonance with the conduction band. Photoluminescence characterization performed on samples of SnO(2) nanobelts at low temperature shows that the basic spectral features of luminescence are in excellent agreement with theoretical predictions.

Vibrational spectroscopy and Density Functional Theory (DFT) quantum chemical calculations, have been used to investigate structure and chemical properties of some fluorinated ethers. A good agreement between experimental and theoretical results has been obtained. Interesting conformational behaviour has been observed and interpreted for C-H bonds in difluoromethyl end groups. These effects help in understanding the chemical behaviour of these compounds, since C-H equilibrium bond length and bond dissociation energy (BDE) can be correlated with vibrational properties. (C) 1998 Elsevier Science S.A. All rights reserved.

Our purpose is to identify a computational level sufficiently dependable and affordable to assess trends in the interaction of a variety of radical or closed shell unsaturated hydro-carbons A adsorbed on soot platelet models B. These systems, of environmental interest, would unavoidably have rather large sizes, thus prompting to explore in this paper the performances of relatively low-level computational methods and compare them with higher-level reference results. To this end, the interaction of three complexes between non-polar species, vinyl radical, ethyne, or ethene (A) with benzene (B) is studied, since these species, involved themselves in growth processes of polycyclic aromatic hydrocarbons (PAHs) and soot particles, are small enough to allow high-level reference calculations of the interaction energy ΔEAB. Counterpoise-corrected interaction energies ΔEAB are used at all stages. (1) Density Functional Theory (DFT) unconstrained optimizations of the A-B complexes are carried out, using the B3LYP-D, ωB97X-D, and M06-2X functionals, with six basis sets: 6-31G(d), 6-311 (2d,p), and 6-311++G(3df,3pd); aug-cc-pVDZ and aug-cc-pVTZ; N07T. (2) Then, unconstrained optimizations by Møller-Plesset second order Perturbation Theory (MP2), with each basis set, allow subsequent single point Coupled Cluster Singles Doubles and perturbative estimate of the Triples energy computations with the same basis sets [CCSD(T)//MP2]. (3) Based on an additivity assumption of (i) the estimated MP2 energy at the complete basis set limit [EMP2/CBS] and (ii) the higher-order correlation energy effects in passing from MP2 to CCSD(T) at the aug-cc-pVTZ basis set, ΔECC-MP, a CCSD(T)/CBS estimate is obtained and taken as a computational energy reference. At DFT, variations in ΔEAB with basis set are not large for the title molecules, and the three functionals perform rather satisfactorily even with rather small basis sets [6-31G(d) and N07T], exhibiting deviation from the computational reference of less than 1 kcal mol(-1). The zero-point vibrational energy corrected estimates Δ(EAB+ZPE), obtained with the three functionals and the 6-31G(d) and N07T basis sets, are compared with experimental D0 measures, when available. In particular, this comparison is finally extended to the naphthalene and coronene dimers and to three π-π associations of different PAHs (R, made by 10, 16, or 24 C atoms) and P (80 C atoms).

The electronic structure of different magnetic states of alpha, beta and gamma modifications of TiCl(3) has been computed employing the density functional theory with periodic boundary conditions and localized Gaussian basis sets. The analysis of the density of the electronic states (DOS) and of the spin density makes it possible to classify these halides as Mott-Hubbard insulators, where the band gap appears a result of large on-site Coulomb interaction. For each crystalline phase, the relative stability of different magnetic states has been analyzed in terms of exchange mechanisms. The electronic population data along with the spin density maps support the assumption of a d(1) Titanium ion in a distorted octahedral crystal field, notwithstanding the not fully ionic character of TiCl(3) modifications. Dispersion forces are particularly important for this material: a classical correction (of the type f(R)/R(6)) has been added to the DFT energies and gradients, providing a good agreement with structural data.

cited By 48; International audience; We present the results of a first principles study on the ordered Ge 0. 50C 0.50 and Sn 0.50C 0.50 cubic alloys. A linear combination of atomic orbitals approach in the framework of density functional theory is employed for total energy calculations in the zincblende phase. A fitting of the energy surface to the equation of state yields the lattice constant of 4.61 and 5.17 Å and the bulk modulus of 181 and 119 GPa for GeC and SnC, respectively. Analysis of band structure suggests a crossover of the nature of the band gap from indirect to direct in going from SiC to GeC to SnC. Although both alloys predicted to be unstable with respect to their elemental components at zero pressure and temperature, GeC appears to become stable at higher pressure. It appears that both the lattice constant and bulk modulus of the ordered alloys do not follow Végard's linear rule, though the calculated dielectric constant of the cubic alloys is approximately the average of the dielectric constant of their elemental components.

Bulk platinum and platinum slabs one to four (111) layers thick have been studied using the HF and DFT CO-LCAO (Hartree-Fock and density functional theory crystalline-orbital and linear-combination-of-atomic-orbitals) CRYSTAL program. The objective of this paper is to test the suitability of slabs of different thicknesses for modelling the (111) surface of platinum. The cohesive properties of the bulk (lattice constant, bulk modulus, cohesive energy) are reported and the electronic structure of the platinum bulk is discussed. The surface and relaxation energies as well as the relaxation distances of the slabs were evaluated. The electronic structure of the slabs is discussed in terms of Mulliken population analysis, the density of states, the band structure and electron-density difference maps. `Initial-state' surface-atom core-level shifts are reported, as well as atomic dipole and quadrupole moments perpendicular to the surface.

cited By 38; International audience; All electron density functional theory calculations were performed on the ordered Ge0.50Sn0.50 alloy in the zinc-blende phase to study its structural, electronic, and optical properties along with its stability with respect to the elemental components. We employed a linear combination of atomic orbitals approach for calculations in which the Bloch functions were constructed as linear combinations of atom-centered Gaussian orbitals. The calculated results show a relative stability of the GeSn alloy in the zinc-blende phase for which the lattice constant and bulk modulus are predicted to be 6.20 Å and 53 GPa, respectively. Analysis of band structure and density of states shows the cubic-ordered alloy to be a direct-gap semiconductor with a small band gap. The optical properties, such as dielectric constant and plasmon energy of the cubic alloy, appear to be about the average of the respective values in its elemental components. © 1999 American Institute of Physics.

International audience; The properties of hcp magnesium are investigated using the density functional method with the linear combination of atomic Orbitals as implemented in the CRYSTAL95 code. The lattice equilibrium parameters and the binding energy have been calculated at the Hartree-Fock level, at the hybrid Hartree-Fock density functional level, and at the Kohn-Sham density functional level using local and non-local exchange and correlation potentials. The electronic properties (band structures, topologies of the Fermi surface, and densities of states) and the elastic constants are computed for each type of functional, and compared to experimental data.

We present an analysis of local or semilocal density functionals for the exchange)correlation energy by decomposing them into their gradients r local Seitz s . . . radius , z relative spin polarization , and s reduced density gradient . We explain the numerical method pertaining to this kind of analysis and present results for a few atoms and ions. The atomic shell structure is prominent, and only the ranges 0 - r - 10 and s 0 - s - 3 are important. The low-density and large-gradient domains, where the approximations for the exchange)correlation energy are least trustworthy, have very little weight. Q 1997 John Wiley & Sons, Inc.

We present electronic and structural parameters for bulk rutile (TiO2) determined by means of different theoretical methods, namely, the periodic Hartree-Fock approach, subsequent post-Hartree-Fock density functional correlation correction, and a linear-combination-of-atomic-orbitals approach based entirely on density functionals. Differences between the use of effective core potentials, a frozen-core treatment, and all-electron calculations are investigated. (C) 1996 John Wiley & Sons, Inc.

All-electron Hartree - Fock and density functional calculations are performed to study the high-pressure phase transitions in gallium nitride and silicon within the framework of the linear combination of atomic orbitals using the Gaussian basis sets. Under high pressure, GaN makes a transition from the wurtzite (semiconducting) to the rock-salt (semiconducting) phase, whereas Si makes a transition from the cubic (semiconducting) to the -tin (metallic) phase. The calculated results suggest that the lattice constants and the bulk moduli can be accurately described by both the methodologies for GaN and Si. Furthermore, both the calculations yield a phase transition pressure for GaN which is in reasonable agreement with the experimental data. However, the transition pressure for Si calculated in the closed-shell (restricted) Hartree - Fock approximation differs significantly from the one calculated using the density functional theory and the experimental data. This is primarily due to the fact that the energy difference between a semiconducting and a metallic state of Si is not well produced in the closed-shell Hartree - Fock approximation.

Density functional theory is taken into account to correct ‘a posteriori’ the total energy calculated with ab initio Hartree-Fock theory. Two models are adopted: the first one is the local density approximation parametrized by Ceperley and Alder while the second one is non-local and corresponds to the formulation proposed by Perdew. The changes in physical properties of ionic sulfide compounds (equilibrium geometry, formation energy, elastic constants, phase transition B1 → B3 in MgS and surface relaxation) associated with the electronic correlation are evaluated.

Numerous density functional theory formulas proposed in the literature are used to compute the total electronic energy of solids, integrating a posteriori functionals of electronic density, obtained with the periodic linear combination of the atomic orbitals Hartree-Fock method. Formation energies, equilibrium geometries and bulk moduli are calculated for a set of 18 covalent, ionic and semi-ionic crystals. A set of 11 density functional models is used. The calculated observables are compared with experimental data; a statistical analysis is performed to compare the models with greater ease.

Infrared spectroscopy in connection with quantum mechanical calculations based on density functional theory (DFT) method have been used for the characterization of fluorinated vinyl ethers. A good correspondence between experimental and calculated spectra has been found. The peculiar behaviour in terms of frequency and intensity parameters relative to the CC stretching normal mode along a series of related compounds has been analysed and interpreted in terms of atomic polar tensor (APT) and equilibrium charge and charge fluxes (ECCFs) models. This study indicates that the IR intensity of the CC stretching mode is almost completely due to the flux terms, suggesting that the presence of fluorine atoms make the charge along CC bond very mobile. This approach, based on comparative analysis of experimental and theoretical data, allows a critical comparison between various chemically related molecules and provides information on the various effects of chemical substitution on the molecular charge distribution.