Search results for "Density functional theory"
showing 10 items of 981 documents
Theoretical study of the molecular structure and the stability of neutral and reduced tetracyanoethylene
2003
Abstract The molecular structure and the stability of neutral, anionic, and dianionic tetracyanoethylene (TCNE) have been studied with MP2, coupled-cluster (CC), and density functional theory (DFT) procedures. The optimized geometries are in agreement with the available experimental data, although significant deviations for the CN bond distance have been obtained at the MP2 level. The adiabatic electron affinity of TCNE calculated with the B3LYP method is overestimated by 0.32 eV. In the light of the CC results, the source of such an overestimation is suggested to lie on the theoretical approach, rather than on a too low experimental value.
Unexpected Scholl Reaction of 6,7,13,14-Tetraarylbenzo[k]tetraphene: Selective Formation of Five-Membered Rings in Polycyclic Aromatic Hydrocarbons
2016
Cyclodehydrogenation is a versatile reaction that has enabled the syntheses of numerous polycyclic aromatic hydrocarbons (PAHs). We now describe a unique Scholl reaction of 6,7,13,14-tetraarylbenzo[k]tetraphene, which "unexpectedly" forms five-membered rings accompanying highly selective 1,2-shift of aryl groups. The geometric and optoelectronic nature of the resulting bistetracene analogue with five-membered rings is comprehensively investigated by single-crystal X-ray, NMR, UV-vis absorption, and cyclic voltammetry analyses. Furthermore, a possible mechanism is proposed to account for the selective five-membered-ring formation with the rearrangement of the aryl groups, which can be ration…
Dicyclopentaannelated Hexa-peri-hexabenzocoronenes with a Singlet Biradical Ground State
2021
Abstract Synthesis of two dicyclopentaannelated hexa‐peri‐hexabenzocoronene (PHBC) regioisomers was carried out, using nonplanar oligoaryl precursors with fluorenyl groups: mPHBC 8 with two pentagons in the “meta”‐configuration was obtained as a stable molecule, while its structural isomer with the “para”‐configuration, pPHBC 16, could be generated and characterized only in situ due to its high chemical reactivity. Both PHBCs exhibit low energy gaps, as reflected by UV‐vis‐NIR absorption and electrochemical measurements. They also show open‐shell singlet ground states according to electron paramagnetic resonance (EPR) measurements and density functional theory (DFT) calculations. The use of…
Certain doping concentrations caused half-metallic graphene
2017
This work is supported by National Natural Science Foundation of China (Grant No. 21173096).
A Molecular Electron Density Theory Study of the Reactivity of Azomethine Imine in [3+2] Cycloaddition Reactions
2017
The electronic structure and the participation of the simplest azomethine imine (AI) in [3+2] cycloaddition (32CA) reactions have been analysed within the Molecular Electron Density Theory (MEDT) using DFT calculations at the MPWB1K/6-311G(d) level. Electron localisation function (ELF) topological analysis reveals that AI has a pseudoradical structure, while the conceptual DFT reactivity indices characterise this TAC as a moderate electrophile and a good nucleophile. The non-polar 32CA reaction of AI with ethylene takes place through a one-step mechanism with low activation energy, 5.3 kcal/mol-1. A bonding evolution theory (BET) study indicates that this reaction takes place through a non-…
Conformations and orientational ordering of semiflexible polymers in spherical confinement.
2017
Semiflexible polymers in lyotropic solution confined inside spherical nanoscopic “containers” with repulsive walls are studied by molecular dynamics simulations and density functional theory, as a first step to model confinement effects on stiff polymers inside of miniemulsions, vesicles, and cells. It is shown that the depletion effects caused by the monomer-wall repulsion depend distinctly on the radius R of the sphere. Further, nontrivial orientational effects occur when R, the persistence length ℓp, and the contour length L of the polymers are of similar magnitude. At intermediate densities, a “shell” of wall-attached chains is forming, such that the monomers belonging to those chains a…
Dynamics of weak interactions in the ligand layer of meta-mercaptobenzoic acid protected gold nanoclusters Au68(m-MBA)32 and Au144(m-MBA)40
2020
Atomically precise metal nanoclusters, stabilized and functionalized by organic ligands, are emerging nanomaterials with potential applications in plasmonics, nano-electronics, bio-imaging, nanocatalysis, and as therapeutic agents or drug carriers in nanomedicine. The ligand layer has an important role in modifying the physico-chemical properties of the clusters and in defining the interactions between the clusters and the environment. While this role is well recognized from a great deal of experimental studies, there is very little theoretical information on dynamical processes within the layer itself. Here, we have performed extensive molecular dynamics simulations, with forces calculated…
Revealing Charge-Transfer Dynamics at Electrified Sulfur Cathodes Using Constrained Density Functional Theory
2021
To understand and control the behavior of electrochemical systems, including batteries and electrocatalysts, we seek molecular-level details of the charge transfer mechanisms at electrified interfaces. Recognizing some key limitations of standard equilibrium electronic structure methods to model materials and their interfaces, we propose applying charge constraints to effectively separate electronic and nuclear degrees of freedom, which are especially beneficial to the study of conversion electrodes, where electronic charge carriers are converted to much slower polarons within a material that is nonmetallic. We demonstrate the need for such an approach within the context of sulfur cathodes …
Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes.
2014
A theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis- and trans-1,2-difluoroethylenes is reported. The results obtained using density functional theory (DFT) combined with large basis sets and gauge-independent atomic orbital calculations were critically compared with experiment and conventional, higher level correlated electronic structure methods. Accurate structural, vibrational, and NMR parameters of difluoroethylenes were obtained using several density functionals combined with dedicated basis sets. B3LYP/6-311++G(3df,2pd) optimized structures of difluoroethylenes closely reproduced experimental geometries and earlier reported b…
Evidence of oblate-prolate shape coexistence in the strongly-deformed nucleus 119Cs
2021
International audience; Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/2[505]11/2− configuration associated with oblate shape. Together with the decoupled πh11/2[541]3/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon p…