Search results for "Density Functional Theory."
showing 10 items of 935 documents
A Theoretical Study of the Relationship between the Electrophilicity ω Index and Hammett Constant σp in [3+2] Cycloaddition Reactions of Aryl Azide/A…
2016
The relationship between the electrophilicity ω index and the Hammett constant σp has been studied for the [2+3] cycloaddition reactions of a series of para-substituted phenyl azides towards para-substituted phenyl alkynes. The electrophilicity ω index—a reactivity density functional theory (DFT) descriptor evaluated at the ground state of the molecules—shows a good linear relationship with the Hammett substituent constants σp. The theoretical scale of reactivity correctly explains the electrophilic activation/deactivation effects promoted by electron-withdrawing and electron-releasing substituents in both azide and alkyne components.
Crystal and molecular structure studies of (Z)-N-methyl-C-4-substituted phenyl nitrones by XRD, DFT, FTIR and NMR methods
2017
Abstract (Z)-N-methyl-C-4-substituted phenyl nitrones –O+N(Me)=C(H)R (Z-2a R = 4-ClC6H4, Z-2b R = 4-NO2C6H4, Z-2c R = 4-CH3OC6H4) were synthesized and characterized by elemental analyses, FTIR, 1H, 13C and DEPT-135 NMR spectroscopy and also by single crystal X-ray diffraction (in the case of Z-2a and Z-2b). The geometries of the nitrone molecules Z-2a, Z-2b and Z-2c and their E-isomers; (E)-N-methyl-C-4-chlorophenyl nitrone E-2a, (E)-N-methyl-C-4-nitrophenyl nitrone E-2b and (E)-N-methyl-C-4-methoxyphenyl nitrone E-2c were optimized using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level of theory. The theoretical vibrational frequencies obtained by DFT calculations are in go…
Structural and electronic properties of β-NaYF4 and β-NaYF4:Ce3+
2020
AP is indebted for a financial support provided by Scientific Research Project grant for Students and Young Researchers Nr. SJZ/2017/3 sponsored at the Institute of Solid State Physics, University of Latvia , while AIP is thankful for the financial support from Latvian Research Council lzp-2018/1-0214 .
First principles calculations of SrZrO3 bulk and ZrO2-terminated (001) surface F centers
2016
Abstract Using a supercell model and B3PW hybrid exchange-correlation functional in the framework of the density functional theory (DFT), as it is implemented in the CRYSTAL computer code, we performed ab initio calculations for the F -center located in the SrZrO 3 bulk and on the ZrO 2 -terminated (001) surface. According to the results of performed relaxation of atoms around the defect, two nearest Zr and four Sr atoms are repulsed, but all oxygen atoms are attracted towards both, the bulk and (001) surface F -center. The displacement magnitudes of atoms surrounding the bulk F -center are smaller than around the (001) surface F -center. The B3PW calculated SrZrO 3 bulk optical band gap (5…
Electron Transfer from Organic Aminophenyl Acid Sensitizers to Titanium Dioxide Nanoparticle Films
2009
Electron transfer from three conjugated amino-phenyl acid dyes to titanium and aluminum oxide nanocrystalline films was studied by using transient absorption spectroscopy with sub 20 fs time-resolution over the visible spectral region. All the dyes attached to TiO2 showed long-lived ground state bleach signals indicative of formation of new species. Global analysis of the transient kinetics of the dyes on TiO2 revealed stimulated emission decays of about 40 fs and less than 300 fs assigned to electron injection. The same dyes on Al2O3 substrates displayed long stimulated emission decays (ns) suggesting that electron transfer is blocked in this high band gap semiconductor. For two of the dye…
Screening the bulk properties and reducibility of Fe-doped Mn2O3 from first principles calculations
2017
Abstract Manganese oxides, particularly Mn 2 O 3 , have demonstrated great potential for oxygen carrier materials in chemical looping applications. The application of these materials in the industrial scale is hindered by thermodynamic restrictions related to the reoxidation process. This disadvantage can be overcome by doping the oxide with a guest cation. Iron is one of the most promising dopants, but the atomic-level understanding of its effects on the properties of α-Mn 2 O 3 is incomplete. Herein, we report a systematic GGA+U study of the bulk properties and reducibility of Fe x Mn 2-x O 3 (0 ≤ x ≤ 2) as a function of Fe dopant concentration. In particular, we focus on a representative…
Structure and dynamics of CaO films: A computational study of an effect of external static electric field
2017
Oxide films play a significant role in a wide range of industrial fields, mostly due to the thickness-dependent variation of their properties. Recently, it has been proposed based on the experimental study that carrier transport in CaO films proceeds via strong phonon excitations with a variable signal depending on the film thickness. In this paper, we report a detailed investigation in the frame of the density functional theory of structural and electronic properties of freestanding and Mo(100)-supported CaO films, as well as phonons therein, as functions of the film thickness and intensity of the external static electric field. Our calculations demonstrate that phonon frequencies negligib…
Q-Chem 2.0: a high-performanceab initio electronic structure program package
2000
ABSTRACT: Q-Chem 2.0 is a new release of an electronic structure programpackage, capable of performing first principles calculations on the ground andexcited states of molecules using both density functional theory and wavefunction-based methods. A review of the technical features contained withinQ-Chem 2.0 is presented. This article contains brief descriptive discussions of thekey physical features of all new algorithms and theoretical models, together withsample calculations that illustrate their performance. c 2000 John Wiley S electronic structure; density functional theory;computer program; computational chemistry Introduction A reader glancing casually at this article mightsuspect on t…
Synthesis and properties of an Au6 cluster supported by a mixed N-heterocyclic carbene–thiolate ligand
2020
The preparation of a novel Au6 cluster bearing a bidentate mixed carbene–thiolate ligand is presented. The length of linker between the central benzimidazole and thiolate has a strong effect on the formation of cluster products, with a C2 chain giving an Au6 cluster, while a C3 chain results in no evidence of cluster formation. Density functional theory analysis predicts a non-metallic cluster with a large HOMO–LUMO (3.2–3.6 eV) and optical gap.
Unraveling materials Berry curvature and Chern numbers from real-time evolution of Bloch states
2019
Materials can be classified by the topological character of their electronic structure and, in this perspective, global attributes immune to local deformations have been discussed in terms of Berry curvature and Chern numbers. Except for instructional simple models, linear response theories have been ubiquitously employed in calculations of topological properties of real materials. Here we propose a completely different and versatile approach to get the topological characteristics of materials by calculating physical observables from the real-time evolving Bloch states: the cell-averaged current density reveals the anomalous velocities whose integration leads to the conductivity quantum. Re…