Theoretical study of the stability of Bep@Rbq core-shell clusters

2013 ◽  
Vol 91 (9) ◽  
pp. 832-838 ◽  
Author(s):  
Yan Sun ◽  
René Fournier
Keyword(s):  
Charge Separation ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Lower Surface ◽  
Outer Shell ◽  
Shell Structures ◽  
Core Shell ◽  
Prototype System ◽  
Surface Charges ◽  
The Difference

Core-shell structures Ap@Bq can be energetically favored in bimetallic clusters when B has a lower surface energy than A, and p and q are chosen such that a single and complete outer shell of q atoms of B can form around the Ap core. If the difference in the electronegativities of A and B is large, one expects significant charge separation between the A core and the B shell. The combination of a closed atomic shell of B atoms and surface charges (core-shell charge separation) should impart stability on this type of Ap@Bq clusters. We report results of density functional theory calculations, including global optimization of cluster geometries, to characterize the prototype system BepRbq. Our calculations show that BepRbq clusters indeed adopt core-shell structures. However, they do not have particularly large surface charges and are unstable against coalescence. Surprisingly, the Rbq outer shell carries a net negative charge. This can be interpreted as the analog, for clusters, of electron spill-out at semi-infinite jellium surfaces, and it probably results from the electrons’ kinetic pressure.

Oxides, Silicides, and Silicates of Zirconium and Hafnium; Density Functional Theory Study

2002 ◽  
Vol 716 ◽  
Author(s):  
Maciej Gutowski ◽  
John E. Jaffe ◽  
Chun-Li Liu ◽  
Matt Stoker ◽  
Anatoli Korkin
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Gate Dielectric ◽  
Density Functional Theory Calculations ◽  
Heat Of Formation ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
Exchange Correlation ◽  
The Difference ◽  
Constituent Elements

AbstractIt is known that the chemistries of hafnium and zirconium are more nearly identical than for any other two congeneric elements. Thus, both zirconia and hafnia, with the dielectric constant K > 20, have emerged as potential replacements for silica (K = 3.9) as a gate dielectric. We report an important difference between the zirconia/Si and hafnia/Si interfaces based on density functional theory calculations with the Perdew-Wang 91 exchange-correlation functional on the oxides, silicides, and silicates of Zr and Hf. The zirconia/Si interface has been found to be unstable with respect to formation of silicides whereas the hafnia/Si interface is stable. The difference between the two interfaces results from the fact that HfO2 is more stable than ZrO2 (i.e. has a larger heat of formation from its constituent elements) by more than 53 kJ/mol. The hafnium silicides, on the other hand, are less stable than zirconium silicides by ca. 20 kJ/mol.

Synthesis, Structure, and Visible Phosphorescence Emission of Novel CuI Coordination Polymers Based on 4,4′-Bis(3-pyridyl)-2,2′-bis(hydroxylmethyl) Biphenyl

2015 ◽  
Vol 68 (2) ◽  
pp. 307 ◽  
Author(s):  
Guo-Xia Jin ◽  
Jian-Ping Ma ◽  
Chuan-Zhi Sun ◽  
Yu-Bin Dong
Keyword(s):  
Coordination Polymers ◽  
Density Functional ◽  
Room Temperature ◽  
Emission Spectra ◽  
Density Functional Theory Calculations ◽  
X Ray Diffraction ◽  
Ligand Charge Transfer ◽  
Yellow Orange ◽  
The Difference ◽  
1D Chains

Four new CuI coordination polymers, [(CuCl)L]n (1), {[(CuCl)2L2]·(H2O)}n (2), [(CuBr)L]n (3), and {[(CuBr)2L2]·(H2O)}n (4), were obtained from a new ligand 4,4′-bis(3-pyridyl)-2,2′-bis(hydroxylmethyl) biphenyl (L) and characterized by single-crystal X-ray diffraction. In 1 and 3, the rhombic [Cu2(μ-X)2] units are connected to each other by the bidentate linkers to form an infinite 1D double chain (X = Cl, Br). Such 1D chains are arranged into a 2D sheet through inter-chain π···π interactions. In 2 and 4, there are similar 1D double chains, but different inter-chain arrangement. Such 1D chains are connected into a 2D layer and further arranged in an ABAB fashion through O–H···X hydrogen bonds. The emission spectra and lifetimes in the microsecond range were measured at room temperature and at 77 K. Complexes 1 and 3 exhibit strong orange and yellow–orange emission in the solid state at room temperature, and were assigned to X-and M-to-ligand charge transfer excited states based on density functional theory calculations. The emission property of 2 and 4 was distinctly different from that of 1 and 3, probably due to the difference in coordination environments of the CuI centres as well as the dissimilar intermolecular arrangement.

New Coordination Architectures of Dithioether Ligand with Silver Salts: Effect of Anions on Complex Structures

2006 ◽  
Vol 59 (1) ◽  
pp. 34 ◽  
Author(s):  
Ya-Bo Xie ◽  
Jian-Rong Li ◽  
Xian-He Bu
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Chain Structure ◽  
X Ray Crystallography ◽  
Silver Salts ◽  
1D Chain ◽  
The Difference ◽  
A Chain ◽  
Dithioether Ligand ◽  
Silver Atoms

Reactions of a flexible dithioether ligand, 2,3-bis(5-methyl-1,3,4-thiadiazole-2-thiomethyl)quinoxaline (L), with AgX (X = ClO4ˉ or PF6ˉ) lead to the formation of two new one-dimensional (1D) silver(i) complexes: {[AgL](ClO4)}∞ 1 and {[Ag2L(CH3OH)](PF6)2(CH3OH)}∞ 2, which have been characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. Although 1 and 2 are synthesized under the same conditions, they take different structures due to the difference in anions in the silver salts. In 1, each ligand supplies three N-donors to bridge two silver atoms to result in a chain structure, and all silver atoms in the chain possess the same coordination geometry. In 2, each ligand gives six N-donors to coordinate to two silver atoms of different geometries, forming a 1D chain. The changes in counteranions affect the coordination mode of the ligand and the geometry of the Ag(i) centre, and consequently give rise to complexes with different structures. The coordination features of the ligand have also been primarily investigated through density functional theory calculations.

scholarly journals Nanoscale Mapping of Heterogeneous Strain and Defects in Individual Magnetic Nanocrystals

Crystals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 658
Author(s):  
Xiaowen Shi ◽  
Ross Harder ◽  
Zhen Liu ◽  
Oleg Shpyrko ◽  
Eric Fullerton ◽  
...  
Keyword(s):  
Uniform Distribution ◽  
Displacement Field ◽  
Density Functional ◽  
Core Region ◽  
Outer Shell ◽  
Core Shell ◽  
Diffractive Imaging ◽  
The Core ◽  
Partial Dislocations ◽  
Distribution Of Magnetization

We map the three-dimensional strain heterogeneity within a single core-shell Ni nanoparticle using Bragg coherent diffractive imaging. We report the direct observation of both uniform displacements and strain within the crystalline core Ni region. We identify non-uniform displacements and dislocation morphologies across the core–shell interface, and within the outer shell at the nanoscale. By tracking individual dislocation lines in the outer shell region, and comparing the relative orientation between the Burgers vector and dislocation lines, we identify full and partial dislocations. The full dislocations are consistent with elasticity theory in the vicinity of a dislocation while the partial dislocations deviate from this theory. We utilize atomistic computations and Landau–Lifshitz–Gilbert simulation and density functional theory to confirm the equilibrium shape of the particle and the nature of the (111) displacement field obtained from Bragg coherent diffraction imaging (BCDI) experiments. This displacement field distribution within the core-region of the Ni nanoparticle provides a uniform distribution of magnetization in the core region. We observe that the absence of dislocations within the core-regions correlates with a uniform distribution of magnetization projections. Our findings suggest that the imaging of defects using BCDI could be of significant importance for giant magnetoresistance devices, like hard disk-drive read heads, where the presence of dislocations can affect magnetic domain wall pinning and coercivity.

Structure of Electronically Reduced N-Donor Bidentate Ligands and Their Heteroleptic Four-Coordinate Zinc Complexes: A Survey of DFT Results

2018 ◽  
Author(s):  
Madanakrishna Katari ◽  
Duncan Carmichael ◽  
Denis Jacquemin ◽  
Gilles Frison
Keyword(s):  
Density Functional ◽  
Structural Changes ◽  
Density Functional Theory Calculations ◽  
Small Degree ◽  
Zinc Complexes ◽  
Hartree Fock ◽  
Exact Exchange ◽  
The Difference ◽  
Geometric Changes

The role of Hartree-Fock exchange in describing the structural changes occurring upon reduction of bipyridine-based ligands and their complexes is investigated in the framework of density functional theory calculations. A set of 4 free ligands in their neutral and radical anionic forms, and 2 of their zinc complexes in their dicationic and monocationic radical forms, is used to compare a large panel of pure, conventional, and long-range corrected hybrid DFT functionals; coupled cluster single and double calculations are used alongside experimental results as benchmarks. Particular attention has been devoted to the magnitude of the change, upon reduction, of the D-parameter, which measures the difference between the Cpy-Cpy and the C-N bond lengths in bipyridine ligand and is known to experimentally correlate with the charge of the ligands. Our results indicate that the structural changes significantly depend on the amount of exact exchange included in the functional. A progressive evolution is observed for the free ligands, whereas two distinct sets of results are obtained for the complexes. Functionals with a small degree of HF exchange, e.g., B3LYP, do not adequately describe geometric changes for the considered species and, quite surprisingly, the same holds for the CC2 method. The best agreement to experimental and CCSD values is obtained with functionals including a significant but not excessive part of exact exchange, e.g., CAM-B3LYP, M06-2X, and wB97X-D. The location of the added electron upon reduction, which depends on the self-interaction error, is used to rationalize these outcomes.<br>

scholarly journals Epoxidation of propene using Au/TiO2: on the difference between H2 and CO as a co-reactant

2017 ◽  
Vol 7 (11) ◽  
pp. 2252-2261 ◽  
Author(s):  
Shamayita Kanungo ◽  
Yaqiong Su ◽  
M. F. Neira d'Angelo ◽  
Jaap C. Schouten ◽  
Emiel J. M. Hensen
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Reducing Gas ◽  
Propene Oxide ◽  
The Difference

The role of the reducing gas in the direct epoxidation of propene to propene oxide (PO) using O2 over a Au/TiO2 catalyst was studied through experiments and density functional theory calculations.

Electrical Characterization of Silicon - Nickel Iron Oxide Heterojunctions

MRS Advances ◽  
2019 ◽  
Vol 4 (41-42) ◽  
pp. 2241-2248
Author(s):  
James N. Talbert ◽  
Samuel R. Cantrell ◽  
Md. Abdul Ahad Talukder ◽  
Luisa M. Scolfaro ◽  
Wilhelmus J. Geerts
Keyword(s):  
Density Functional ◽  
Electrical Characterization ◽  
Density Functional Theory Calculations ◽  
Oxygen Flow ◽  
Low Oxygen ◽  
Nickel Iron ◽  
Specific Contact ◽  
The Difference ◽  
P Type

ABSTRACTThe electrical properties of Radio Frequency Sputtered NiFeO and NiO films deposited on n and p-type Silicon is investigated for two different oxygen flows. Rectifying properties for Ni0.8Fe0.2O1+ α on n-Si showed Iforward/Ireverse &gt;10,000 for α&gt;0 and Iforward/Ireverse &gt;50 for α&lt;0. Both types of devices have opposite forward biases. Results suggest that NiFeO sputtered at high oxygen flow is p-type. For NiO and NiFeO on p-Si no strong rectifying properties were observed. The specific contact resistivity of Pt/Ni0.9Fe0.1O1+ α (α&gt;0) was estimated from the difference between the two and four-point probe resistances (0.0007 ± 0.0003 Ω cm2). Using density functional theory calculations, density of state and charge density plots were obtained for systems modelled after experiment, showing that states introduced by O vacancies in NiFeO are localized and prefer locations near Ni explaining the observed hysteresis effects in the IV curves of devices sputtered at low oxygen flow.

Structural, spectroscopic (FT-IR, FT-Raman, NMR) and computational analysis (DOS, NBO, Fukui) of 3,5-dimethylisoxazole and 4-(chloromethyl)-3,5-dimethylisoxazole: A DFT study

2016 ◽  
Vol 15 (05) ◽  
pp. 1650039 ◽  
Author(s):  
T. Kavitha ◽  
G. Velraj
Keyword(s):  
Density Functional ◽  
Computational Analysis ◽  
Chemical Shifts ◽  
Vibrational Analysis ◽  
Density Functional Theory Calculations ◽  
Basis Set ◽  
Reactivity Descriptors ◽  
The Density Functional Theory ◽  
Ft Ir ◽  
The Difference

The theoretical and computational analysis of two isoxazole derivatives 3,5-dimethylisoxazole and 4-chloromethyl-3,5-dimethylisoxazole were carried out along with some of the experimental evidences. The density functional theory calculations of these compounds were done with DFT/B3LYP/6-31+G(d,p) basis set using Gaussian 09 software. From the DFT calculations, the optimization geometry, vibrational analysis, electronic properties, local reactivity descriptors, natural bond orbitals, and other structural properties of the title compounds were elucidated. The chemical shifts of every C and H atom of the title compounds were calculated using Gauge Independent Atomic orbitals (GIAO) method for both proton and carbon NMR spectra. The molecular electrostatic potential of DMI has been found out and the difference in MEP on addition of chloromethyl group is also discussed. The hyperpolarizability calculations of the investigated molecules shows that the nonlinear optical activity of CDMI is greater when compared to DMI.

Boron clusters with 46, 48, and 50 atoms: competition among the core–shell, bilayer and quasi-planar structures

Nanoscale ◽  
2017 ◽  
Vol 9 (37) ◽  
pp. 13905-13909 ◽  
Author(s):  
Linwei Sai ◽  
Xue Wu ◽  
Nan Gao ◽  
Jijun Zhao ◽  
R. Bruce King
Keyword(s):  
Genetic Algorithm ◽  
Density Functional Theory ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Global Search ◽  
Core Shell ◽  
Functional Theory ◽  
Boron Clusters ◽  
The Core ◽  
Planar Structures

Using a genetic algorithm combined with density functional theory calculations, we perform a global search for the lowest-energy structures of Bnclusters withn= 46, 48, 50.

scholarly journals Structural Features of Y2O2SO4 via DFT Calculations of Electronic and Vibrational Properties

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3246
Author(s):  
Aleksandr S. Oreshonkov ◽  
Yuriy G. Denisenko
Keyword(s):  
Density Functional ◽  
Dielectric Material ◽  
Electronic Band Structure ◽  
Density Functional Theory Calculations ◽  
Structural Features ◽  
Spectral Lines ◽  
Partial Density ◽  
X Ray Diffraction ◽  
Electronic Band ◽  
The Difference

The traditional way for determination of molecular groups structure in crystals is the X-Ray diffraction analysis and it is based on an estimation of the interatomic distances. Here, we report the analysis of structural units in Y2O2SO4 using density functional theory calculations of electronic properties, lattice dynamics and experimental vibrational spectroscopy. The Y2O2SO4 powder was successfully synthesized by decomposition of Y2(SO4)3 at high temperature. According to the electronic band structure calculations, yttrium oxysulfate is a dielectric material. The difference between the oxygen–sulfur and oxygen–yttrium bond nature in Y2O2OS4 was shown based on partial density of states calculations. Vibrational modes of sulfur ions and [Y2O22+] chains were obtained theoretically and corresponding spectral lines observed in experimental Infrared and Raman spectra.

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