Search results for "Density Functional Theory."

Experimental and DFT Studies on Competitive Heterocyclic Rearrangements. 3. A Cascade Isoxazole−1,2,4-Oxadiazole−Oxazole Rearrangement

2008

The thermal rearrangements of 3-acylamino-5-methylisoxazoles 1 have been investigated under basic and neutral conditions and interpreted with the support of computational data. The density functional theory (DFT) study on the competitive routes available for the base-catalyzed thermal rearrangement of isoxazoles 1 showed that the Boulton-Katritzky (BK) rearrangement, producing the less stable 3-acetonyl-1,2,4-oxadiazoles 5, is a much more favored process than either the migration-nucleophilic attack-cyclization (MNAC) or the ring contraction-ring expansion (RCRE). In turn, an increase in reaction temperature will promote the MNAC of oxadiazoles 5, producing the more stable 2-acylaminooxazol…

Ferroelectric polarization switching induced from water adsorption in BaTiO 3 ultrathin films

2020

The influence of water on the out-of-plane polarization of ${\mathrm{BaTiO}}_{3}$ (BTO) ultrathin films is studied by means of density functional theory calculations. The adsorption is investigated for different coverages on both terminations of BTO with, for each case, all possible states of polarization, namely, paraelectric, polarized upward, and polarized downward. We thus demonstrate different behavior as a function of the termination. While ${\mathrm{H}}_{2}\mathrm{O}$ adsorbs only dissociatively on the BaO termination, with a reinforced interaction compared to BTO without out-of-plane polarization, only molecular adsorption is observed on the ${\mathrm{TiO}}_{2}$ termination. In addi…

Effect of ion exchange capacity and water uptake on hydroxide transport in PSU-TMA membranes: A DFT and molecular dynamics study

2020

Abstract Anion Exchange Membranes (AEMs) are nowadays used in a very wide range of different applications, from electrodialytic systems for water treatment, to Fuel Cells for energy generation. In many of these cases, the AEM is in contact with water molecules, either in aqueous or gas phase, which can strongly interact with the AEM polymer, thus affecting membrane properties. The role of water in fully swollen AEM and its effect on the diffusion of hydroxide is the focus of this work. Density Functional Theory (DFT) based calculations were merged with Molecular Dynamics (MD) simulations coming to a more accurate description of the ionic exchange capacity effect on the hydroxide ion diffusi…

Quantitative Analysis of the Interactions of Metal Complexes and Amphiphilic Systems: Calorimetric, Spectroscopic and Theoretical Aspects.

2022

Metals and metal-based compounds have many implications in biological systems. They are involved in cellular functions, employed in the formation of metal-based drugs and present as pollutants in aqueous systems, with toxic effects for living organisms. Amphiphilic molecules also play important roles in the above bio-related fields as models of membranes, nanocarriers for drug delivery and bioremediating agents. Despite the interest in complex systems involving both metal species and surfactant aggregates, there is still insufficient knowledge regarding the quantitative aspects at the basis of their binding interactions, which are crucial for extensive comprehension of their behavior in sol…

Experimental and theoretical study of stereoelectronic and H-bond control of reactivity in α- and β-methyl d-glucopyranoside ozonolysis

1998

Abstract The topography of the molecular electrostatic potential (MEP) of α and β anomers of methyl d -glucopyranosides has been used to analyze the reactivity of these species towards electrophilic attack and to complete the results we obtained during the ozonation reaction. Molecular mechanics (MM) and molecular dynamics (MD) simulations have been performed to screen the conformational space of α- and β-methyl d -glucopyranosides in order to determine the chair conformations which correspond to a global minimum energy conformation. Density Functional Theory (DFT) (Faststructure) and PM3 (semiempirical) calculations have been carried out to refine the geometries of the 4 C 1 and 1 C 4 chai…

ChemInform Abstract: Electrochemical Synthesis of 2-Arylimino-4,5-di(2-furyl)-1,3-dioxoles and (E)-1,2-Di(2-furyl)vinylene Bis(N-arylchloroformimidat…

2009

Abstract Cathodic reductions of 2,2′-furils in the presence of N-arylcarbonimidoyl dichlorides lead to 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles in high yields, along with minor amounts of (E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP density functional theory methods have been applied to the determination of molecular geometries and to study the topomerization mechanism of aryliminodioxoles. The molecular structure of (E)-1,2-di(2-furyl)vinylene bis[N-(2-chloro-4-methylphenyl)chloroformimidate] has been determined by X-ray crystallography and compared with the calculated structure.

Diene-Containing Half-Sandwich MoIII Complexes as Ethylene Polymerization Catalysts: Experimental and Theoretical Studies

2001

International audience; Seventeen-electron compounds of Mo III having the general formula [(h 5-C 5 R 5)Mo(h 4-diene)X 2 ] (R H, Me; diene butadiene, iso-prene, or 2,3-dimethylbutadiene; X Cl, CH 3) are a new class of ethylene polymerization catalysts. The polyethy-lene obtained shows a bimodal distribution , the major weight fraction being characterized by very long (M around 10 6) and highly linear polymer chains. The newly prepared pentamethylcyclo-pentadienyl (Cp*) derivatives are more active than the cyclopentadienyl (Cp) derivatives, but much less active than previously investigated niobium III compounds having the same stoichiometry. On the other hand, the turnover frequency of the a…

2015

AbstractWhile understanding the properties of materials under stress is fundamentally important, designing experiments to probe the effects of large tensile stress is difficult. Here tensile stress is created in thin films of potassium (up to 4 atomic layers) by epitaxial growth on a rigid support, graphite. We find that this “simple” metal shows a long-range, periodic “herringbone” reconstruction, observed in 2- and 3- (but not 1- and 4-) layer films by low-temperature scanning tunneling microscopy (STM). Such a pattern has never been observed in a simple metal. Density functional theory (DFT)simulations indicate that the reconstruction consists of self-aligned stripes of enhanced atom den…

Electron microscopy of gold nanoparticles at atomic resolution

2014

Detailed structure of a gold nanoparticle Adding only a few atoms or changing the capping ligand can dramatically change the structure of individual metal nanoparticles. Azubel et al. used aberration-corrected transmission electron microscopy to derive a three-dimensional reconstruction of water-soluble gold nanoparticles. Small-angle x-ray scattering and other techniques have also corroborated this model. They used this to determine the atomic structure, which compared favorably with density functional theory calculations, without assuming any a priori structural knowledge or the use of model fitting. Science , this issue p. 909

On deterministic solutions for multi-marginal optimal transport with Coulomb cost

2022

In this paper we study the three-marginal optimal mass transportation problem for the Coulomb cost on the plane $\R^2$. The key question is the optimality of the so-called Seidl map, first disproved by Colombo and Stra. We generalize the partial positive result obtained by Colombo and Stra and give a necessary and sufficient condition for the radial Coulomb cost to coincide with a much simpler cost that corresponds to the situation where all three particles are aligned. Moreover, we produce an infinite class of regular counterexamples to the optimality of this family of maps.