Search results for "Density Functional Theory."
showing 10 items of 935 documents
High-Pressure Synthesis of Novel Boron Oxynitride B6N4O3 with Sphalerite Type Structure
2015
A novel crystalline boron oxynitride (BON) phase has been synthesized under static pressures exceeding 15 GPa and temperatures above 1900 °C, from molar mixtures of B2O3 and h-BN. The structure and composition of the synthesized product were studied using high-resolution transmission electron microscopy, electron diffraction, automated diffraction tomography, energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS). BON shows a hexagonal cell (R3m, Z = 3) with lattice parameters a = 2.55(5) A and c = 6.37(13) A, and a crystal structure closely related to the cubic sphalerite type. The EELS quantification yielded 42 at % B, 35 at % N, and 23 at % O (B:N:O ≈ 6:4:3). E…
Excited state absorption spectra of dissolved and aggregated distyrylbenzene: A TD-DFT state and vibronic analysis
2017
Made available in DSpace on 2018-12-11T17:33:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-07-21 Federación Española de Enfermedades Raras Ministerio de Economía y Competitividad A time-dependent density functional theory study is performed to reveal the excited state absorption (ESA) features of distyrylbenzene (DSB), a prototype π-conjugated organic oligomer. Starting with a didactic insight to ESA based on simple molecular orbital and configuration considerations, the performance of various density functional theory functionals is tested to reveal the full vibronic ESA features of DSB at short and long probe delay times. UNESP-Universidade Estadual Paulista POSMAT-Graduate Pr…
Dipoles in 4,12,4-graphyne
2021
Abstract In present work, B-N pairs as dipole source were introduced into 4,12,4-graphyne. According to the density functional theory (DFT) simulations, the electronic configurations of the doped 4,12,4-graphyne systems were significantly modified owing to the built-in electric fields caused by the B-N dipoles. Different B-N concentrations and arrangements can alter the electronic structure of 4,12,4-graphyne. Consequently, an obvious in-plane piezoelectricity can also be induced. Moreover, the direct band gap can be delicately modulated from 150 meV to 660 meV at PBE level. The B-N dipoles can also greatly enhance the light absorption instead of shifting the absorption region. According to…
Plasmon Excitations in Mixed Metallic Nanoarrays
2019
Features of the surface plasmon from macroscopic materials emerge in molecular systems, but differentiating collective excitations from single-particle excitations in molecular systems remains elusive. The rich interactions between single-particle electron-hole and collective electron excitations produce phenomena related to the chemical physics aspects within the atomic array. We study the plasmonic properties of atomic arrays of noble (Au, Ag, and Cu) and transition-metal (Pd, Pt) homonuclear chains using time-dependent density functional theory and their Kohn-Sham transition contributions. The response to the electromagnetic radiation is related to both the geometry-dependent confinement…
First-principles comparative study of perfect and defective CsPbX3 (X = Br, I) crystals
2020
We thank R. Merkle for numerous fruitful discussions and G. Siegle for experimental assistance. This study was partly supported by the M-ERA-NET project SunToChem (EK). Calculations were performed using computational facilities of St. Petersburg State University and Max Planck Institute for Solid State Research. Open Access funding provided by the Max Planck Society.
Atomically Precise, Thiolated Copper–Hydride Nanoclusters as Single-Site Hydrogenation Catalysts for Ketones in Mild Conditions
2019
Copper-hydrides are known catalysts for several technologically important reactions such as hydrogenation of CO, hydroamination of alkenes and alkynes, and chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols. Stabilizing copper-based particles by ligand chemistry to nanometer scale is an appealing route to make active catalysts with optimized material economy; however, it has been long believed that the ligand-metal interface, particularly if sulfur-containing thiols are used as stabilizing agent, may poison the catalyst. We report here a discovery of an ambient-stable thiolate-protected copper-hydride nanocluster [Cu25H10(SPhCl2)18]3- that readily catalyzes hydrogen…
Ab initiocalculations of theFcenters in MgF2bulk and on the (001) surface
2012
We present and discuss the results of atomic and electronic structure calculations of the F centers in MgF2 bulk and on the (001) surface. The calculations are based on the B3PW Hartree–Fock and density functional theory hybrid exchange-correlation functional. Most of the electronic density of a missing fluorine ion is localized in the bulk vacancy and a little bit less—in a surface vacancy. It is shown that the electronic F center is a deep donor. The lattice distortion and defect formation energy on the neutral (001) surface and in the bulk are also compared.
The Intrinsic Defects, Disordering, and Structural Stability of BaxSr1–xCoyFe1–yO3−δ Perovskite Solid Solutions
2012
First principles density functional theory modeling of point defects and structural disordering in BaxSr1–xCoyFe1–yO3−δ (BSCF) perovskites reveals that the material tends to decompose at low temperatures into a mixture of cubic and hexagonal perovskite and/or oxide phases. Special attention is paid to elucidating the effects of oxygen nonstoichiometry on cubic and hexagonal phase stability, decomposition energies, and oxygen vacancy formation energies. The observed lattice instability is likely to negate the advantages of the fast oxygen transport chemistry and impede the applicability of BSCF in solid oxide fuel cells and oxygen separation ceramic membranes. The general methodology present…
Hole-Transporting Materials for Perovskite Solar Cells Employing an Anthradithiophene Core
2021
A decade after the report of the first efficient perovskite-based solar cell, development of novel hole-transporting materials (HTMs) is still one of the main topics in this research field. Two of the main advance vectors of this topic lie in obtaining materials with enhanced hole-extracting capability and in easing their synthetic cost. The use of anthra[1,9-bc:5,10-b'c']dithiophene (ADT) as a flat π-conjugated frame for bearing arylamine electroactive moieties allows obtaining two novel highly efficient HTMs from very cheap precursors. The solar cells fabricated making use of the mixed composition (FAPbI3)0.85(MAPbBr3)0.15 perovskite and the novel ADT-based HTMs show power conversion effi…
Chiral mesophases of hydrogen-bonded liquid crystals
2020
The chiral induction in hydrogen-bonded liquid crystals is investigated. The experimental study was accompanied by detailed density functional theory calculations and variable-temperature solid-state deuteron NMR measurements indicating that interactions between the linking groups of the hydrogen-bond accepting unit play a key role in the chiral induction.