Structural Aspects of Magnetic Coupling in CaCu3Mn4O12 and CaCu3Ti4P12

2002 ◽  
Vol 718 ◽  
Author(s):  
M. D. Johannes ◽  
W. E. Pickett ◽  
R. Weht
Keyword(s):  
First Principles ◽  
Exchange Coupling ◽  
Density Functional ◽  
Energy Gap ◽  
Three Dimensional ◽  
Magnetic Coupling ◽  
Superexchange Coupling ◽  
Distinct Temperature ◽  
Insight Into ◽  
Structural Aspects

AbstractTwo perovskite-derived materials, CaCu3Mn4O12, have drawn much recent interest due to their magnetoresistive, dielectric, and mafnetoelectronic characteristics. Here we present initial theoretical insights into each of these points, based on first principles, density functional based calculations. Our results predict CCMO to have a spin-asymmetric energy gap, which leads to distinct temperature- and magnetic field-dependent changes in properties, and helps to account for its observed negative magnetoresistivity. We have studied CCTO primarily to gain insight into the exchange coupling in both these compounds, where the conventional superexchange coupling vanishes by symmetry for both nearest and next nearest Cu-Cu neighbors, a consequence of the structure. In CCTO, it is necessary to go 5th Cu-Cu neighbors to obstain a (superexchange) coupling that can provide the coupling necessary to give three dimensional order. Non-superexchange mechanisms may be necessary to describe the magnetic coupling in this structural clss.

scholarly journals Mono- and Bi-Molecular Adsorption of SF6 Decomposition Products on Pt Doped Graphene: A First-Principles Investigation

2018 ◽  
Vol 8 (10) ◽  
pp. 2010 ◽  
Author(s):  
Yongqian Wu ◽  
Shaojian Song ◽  
Dachang Chen ◽  
Xiaoxing Zhang
Keyword(s):  
Single Molecule ◽  
First Principles ◽  
Density Functional ◽  
Energy Gap ◽  
Adsorption Parameters ◽  
Functional Theory ◽  
Decomposition Products ◽  
Before And After ◽  
Doped Graphene ◽  
Sf6 Decomposition

Based on the first-principles of density functional theory, the SF6 decomposition products including single molecule (SO2F2, SOF2, SO2), double homogenous molecules (2SO2F2, 2SOF2, 2SO2) and double hetero molecules (SO2 and SOF2, SO2 and SO2F2, SOF2 and SO2F2) adsorbed on Pt doped graphene were discussed. The adsorption parameters, electron transfer, electronic properties and energy gap was investigated. The adsorption of SO2, SOF2 and SO2F2 on the surface of Pt-doped graphene was a strong chemisorption process. The intensity of chemical interactions between the molecule and the Pt-graphene for the above three molecules was SO2F2 > SOF2 > SO2. The change of energy gap was also studied and according to the value of energy gap, the conductivity of Pt-graphene before and after adsorbing different gas molecules can be evaluated.

Nano-sized nickel catalyst for deep hydrogenation of lignin monomers and first-principles insight into the catalyst preparation

2017 ◽  
Vol 5 (8) ◽  
pp. 3948-3965 ◽  
Author(s):  
Shi-Chao Qi ◽  
Lu Zhang ◽  
Hisahiro Einaga ◽  
Shinji Kudo ◽  
Koyo Norinaga ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Full Range ◽  
Catalyst Preparation ◽  
Ni Catalyst ◽  
Borohydride Reduction ◽  
Functional Theory ◽  
Pyridine Complex ◽  
Insight Into

A type of nano-sized Ni catalyst supported by ZSM-5 zeolite for the deep hydrogenation of lignin monomers is prepared by borohydride reduction of a Ni2+–pyridine complex in ethanol. The mechanism of the borohydride reduction over the full range from Ni2+ to Ni0 is calculated by applying density functional theory.

First-Principles Study of the Calcium Insertion in Layered and Non-Layered Phases of Vanadia

MRS Advances ◽  
2018 ◽  
Vol 3 (60) ◽  
pp. 3507-3512 ◽  
Author(s):  
Daniel Koch ◽  
Sergei Manzhos
Keyword(s):  
First Principles ◽  
Vanadium Dioxide ◽  
Calcium Ion ◽  
Density Functional ◽  
Host Lattice ◽  
Functional Theory ◽  
Suitable Material ◽  
Low Concentrations ◽  
Oxide Phases ◽  
Insight Into

ABSTRACTWe investigate the insertion energetics of Ca at low concentrations in four promising vanadium oxide phases (α and δ vanadium pentoxide (V2O5) polymorphs as well as rutile- (R) and bronze-type (B) vanadium dioxide (VO2)) using density functional theory (DFT). We find α-V2O5 to be the most suitable material for an application as cathode, driven by a stable coordinative environment, while VO2(R) does not exhibit a stable low-concentration CaxVO2 phase due to severe distortions of the host lattice due to the large calcium ion. The results provide insight into the possibility of employing these phases as active cathode materials of Ca-ion batteries.

Structural aspects of agonism and antagonism in the oestrogen receptor

2000 ◽  
Vol 28 (4) ◽  
pp. 396-400 ◽  
Author(s):  
A. C. W. Pike ◽  
A. M. Brzozowski ◽  
J. Walton ◽  
R. E. Hubbard ◽  
T. Bonn ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Oestrogen Receptor ◽  
Three Dimensional ◽  
Receptor Activation ◽  
Structural Basis ◽  
Diverse Range ◽  
Antagonist Action ◽  
Receptor Agonists And Antagonists ◽  
Insight Into ◽  
Structural Aspects

We have determined the three-dimensional structures of both α- and β-forms of the ligand-binding domain of the oestrogen receptor (ER) in complexes with a range of receptor agonists and antagonists. Here, we summarize how these structures provide both an understanding of the ER's distinctive pharmacophore and a rationale for its ability to bind a diverse range of chemically distinct compounds. In addition, these studies provide a unique insight into the mechanisms that underlie receptor activation, as well as providing a structural basis for the antagonist action of molecules, such as raloxifene.

A MOLECULAR DIODE BASED ON CONJUGATED CO-OLIGOMERS

2006 ◽  
Vol 05 (04n05) ◽  
pp. 535-540
Author(s):  
PING BAI ◽  
CHEE CHING CHONG ◽  
ER PING LI ◽  
ZHIKUAN CHEN
Keyword(s):  
Density Functional Theory ◽  
Spatial Orientation ◽  
First Principles ◽  
Density Functional ◽  
Infinite System ◽  
Energy Gap ◽  
Functional Theory ◽  
Molecular Diode ◽  
Current Voltage ◽  
P Type

A molecular diode based on a conjugated co-oligomer composed of p-type and n-type segments is investigated using the first principles method. The co-oligomer is connected to Au electrodes to form an Au –oligomer– Au system. The infinite system is dealt with a finite structure confined in a device region and effects from semi-infinite electrodes. Density functional theory and nonequilibrium Green's function are used to describe the device region self-consistently. The current–voltage (I–V) characteristics of the constructed system are calculated and a rectification behavior is observed. The energy gap and the spatial orientation of molecular orbitals, and the transmission functions are calculated to analyze the I–V characteristics of the molecular diode.

FIRST-PRINCIPLES STUDY OF THE ELECTRONIC, LINEAR, AND NONLINEAR OPTICAL PROPERTIES OF Li(Nb, Ta)O3

2010 ◽  
Vol 24 (32) ◽  
pp. 6277-6290 ◽  
Author(s):  
SULEYMAN CABUK
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Nonlinear Optical ◽  
Energy Gap ◽  
Local Density ◽  
Theoretical Calculations ◽  
Total Density ◽  
Functional Theory ◽  
Experimental Values ◽  
Electron Energy Loss

We investigate the energy band structure, total density of states, the linear, nonlinear optical (NLO) response, and the electron energy-loss spectrum for Li(Nb, Ta)O 3 using first principles calculations based on density functional theory in its local density approximation. Our calculation shows that these compounds have similar structures. The indirect band gaps of 3.39 eV (LiNbO3) and 3.84 eV (LiTaO3) at the Γ–Z direction in the Brillouin zone are found. A simple scissor approximation is applied to adjust the band energy gap from the calculations to match the experimental values. The optical spectra are analyzed and the origins of some of the peaks in the spectra are discussed in terms of calculated electronic structure. Calculations are reported for the frequency-dependent complex second-order NLO susceptibilities [Formula: see text] up to 10 eV and for zero-frequency limit [Formula: see text]. The results are compared with the theoretical calculations and the available experimental data.

First-principles study on codoping effect to enhance photocatalytic activity of anatase TiO2

2017 ◽  
Vol 31 (06) ◽  
pp. 1750036
Author(s):  
Yujie Bai ◽  
Qinfang Zhang ◽  
Fubao Zheng ◽  
Yun Yang ◽  
Qiangqiang Meng ◽  
...  
Keyword(s):  
Visible Light ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Energy Gap ◽  
Density Functional Theory Calculations ◽  
Band Edge ◽  
Electron Hole ◽  
Functional Theory ◽  
Rich Condition

Codopant is an effective approach to modify the bandgap and band edge positions of transition metal oxide. Here, the electronic structures as well as the optical properties of pristine, mono-doped (N/P/Sb) and codoped (Sb, N/P) anatase TiO2 have been systematically investigated based on density functional theory calculations. It is found that mono-doped TiO2 exhibits either unoccupied or partially occupied intermediate state within the energy gap, which promotes the recombination of electron-hole pairs. However, the presence of (Sb, N/P) codopant not only effectively reduces the width of bandgap by introducing delocalized occupied intermediate states, but also adjusts the band edge alignment to enhance the hydrogen evolution activity of TiO2. Moreover, the optical absorption spectrum for (Sb, N/P) codoped TiO2, which is favored under oxygen-rich condition, demonstrates the improvement of its visible light absorption. These findings will promote the potential application of (Sb, N/P) codoped TiO2 photocatalysis for water splitting under visible light irradiation.

scholarly journals Determination of Silicon Electrical Properties Using First Principles Approach

2021 ◽  
Vol 2129 (1) ◽  
pp. 012056
Author(s):  
Uda Hashim ◽  
Tijjani Adam ◽  
M N Afnan Uda ◽  
M N A Uda
Keyword(s):  
Band Gap ◽  
Silicon Nanowires ◽  
First Principles ◽  
Density Functional ◽  
Energy Gap ◽  
Silicon Nanowire ◽  
Continuum Theory ◽  
Simple Extrapolation ◽  
Structure Calculations

Abstract Silicon nanowires have attracted attention as basis for reconfigurable electronics. However, as the size decreases, the electronic properties of the nanowires vary as a result of confinement, strain and crystal topology effects. Thus, at the thin diameter regime the band gap of Silicon nanowires can no longer be derived from a simple extrapolation of the isotropic bulk behaviour. This study compares band gap parameters in sub 10nm nanowires obtained from first-principles density-functional band structure calculations with extrapolations using continuum theory in order to rationalize the changes of the overall conductance, resistance and band gap. The device consists of silicon nanowire of size between 1 nm to 6nm. The results indicate an increase of, both the energy gap and the resistance along with reduced conductivity for the thinnest wires and a dependence on the crystal orientation with gaps reaching up to 4.3 eV along <111>, 4.0 eV along <110>, and 3.7 along <100>.

scholarly journals Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

2020 ◽  
Author(s):  
Aqeel A. Hussein ◽  
Ahmed Al-Yasari ◽  
Yumiao Ma
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Single Electron ◽  
Hypervalent Iodine ◽  
Functional Theory ◽  
Rate Determining Step ◽  
Before And After ◽  
Electron Reduction ◽  
Dynamics Simulations ◽  
Insight Into

A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

scholarly journals Crystal structure, Hirshfeld surface analysis and DFT studies of 2-[(2-hydroxy-5-methylbenzylidene)amino]benzonitrile

2020 ◽  
Vol 76 (8) ◽  
pp. 1195-1200
Author(s):  
Md. Serajul Haque Faizi ◽  
Emine Berrin Cinar ◽  
Alev Sema Aydin ◽  
Erbil Agar ◽  
Necmi Dege ◽  
...  
Keyword(s):  
Surface Analysis ◽  
Density Functional ◽  
Energy Gap ◽  
Condensation Reaction ◽  
Three Dimensional ◽  
Hirshfeld Surface ◽  
Hirshfeld Surface Analysis ◽  
Orthorhombic Space Group ◽  
Compound C ◽  
Dimensional Network

The title compound, C15H12N2O, was synthesized by condensation reaction of 2-hydroxy-5-methylbenzaldehyde and 2-aminobenzonitrile, and crystallizes in the orthorhombic space group Pbca. The phenol ring is inclined to the benzonitrile ring by 25.65 (3)°. The configuration about the C=N bond is E, stabilized by a strong intramolecular O—H...N hydrogen bond that forms an S(6) ring motif. In the crystal, C—H...O and C—H...N interactions lead to the formation of sheets perpendicular to the a axis. C—H...π interactions, forming polymeric chains along the a-axis direction, connect these sheets into a three-dimensional network. A Hirshfeld surface analysis indicates that the most important contributions for the packing arrangement are from H...H and C...H/H...C interactions. The density functional theory (DFT) optimized structure at the B3LYP/6–311 G(d,p) level is compared with the experimentally determined molecular structure and the HOMO–LUMO energy gap is given.

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