scholarly journals Defects and Dopants in CaFeSi2O6: Classical and DFT Simulations

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1285 ◽  
Author(s):  
Navaratnarajah Kuganathan ◽  
Alexander Chroneos
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Electrode Materials ◽  
Ion Diffusion ◽  
Reaction Energy ◽  
Functional Theory ◽  
Ion Migration ◽  
Process Formation ◽  
Calculated Activation Energy ◽  
Calculated Activation

Calcium (Ca)-bearing minerals are of interest for the design of electrode materials required for rechargeable Ca-ion batteries. Here we use classical simulations to examine defect, dopant and transport properties of CaFeSi2O6. The formation of Ca-iron (Fe) anti-site defects is found to be the lowest energy process (0.42 eV/defect). The Oxygen and Calcium Frenkel energies are 2.87 eV/defect and 4.96 eV/defect respectively suggesting that these defects are not significant especially the Ca Frenkel. Reaction energy for the loss of CaO via CaO Schottky is 2.97 eV/defect suggesting that this process requires moderate temperature. Calculated activation energy of Ca-ion migration in this material is high (>4 eV), inferring very slow ionic conductivity. However, we suggest a strategy to introduce additional Ca2+ ions in the lattice by doping trivalent dopants on the Si site in order to enhance the capacity and ion diffusion and it is calculated that Al3+ is the favourable dopant for this process. Formation of Ca vacancies required for the CaO Schottky can be facilitated by doping of gallium (Ga) on the Fe site. The electronic structures of favourable dopants were calculated using density functional theory (DFT).

scholarly journals Na-ion diffusion in a NASICON-type solid electrolyte: a density functional study

2016 ◽  
Vol 18 (39) ◽  
pp. 27226-27231 ◽  
Author(s):  
Kieu My Bui ◽  
Van An Dinh ◽  
Susumu Okada ◽  
Takahisa Ohno
Keyword(s):  
Density Functional Theory ◽  
Solid Electrolyte ◽  
Electronic Structures ◽  
Density Functional ◽  
Diffusion Mechanism ◽  
Functional Study ◽  
Ion Diffusion ◽  
Functional Theory ◽  
Density Functional Study ◽  
Nasicon Type

Based on density functional theory, we have systematically studied the crystal and electronic structures, and the diffusion mechanism of the NASICON-type solid electrolyte Na3Zr2Si2PO12.

scholarly journals Defects, Diffusion, and Dopants in Li2Ti6O13: Atomistic Simulation Study

Materials ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 2851 ◽  
Author(s):  
Navaratnarajah Kuganathan ◽  
Sashikesh Ganeshalingam ◽  
Alexander Chroneos
Keyword(s):  
Electronic Structures ◽  
Atomistic Simulation ◽  
Density Functional ◽  
High Capacity ◽  
Ion Diffusion ◽  
Functional Theory ◽  
Energy Process ◽  
Defect Energy ◽  
Li Ion ◽  
Isovalent Dopant

In this study, force field-based simulations are employed to examine the defects in Li-ion diffusion pathways together with activation energies and a solution of dopants in Li2Ti6O13. The lowest defect energy process is found to be the Li Frenkel (0.66 eV/defect), inferring that this defect process is most likely to occur. This study further identifies that cation exchange (Li–Ti) disorder is the second lowest defect energy process. Long-range diffusion of Li-ion is observed in the bc-plane with activation energy of 0.25 eV, inferring that Li ions move fast in this material. The most promising trivalent dopant at the Ti site is Co3+, which would create more Li interstitials in the lattice required for high capacity. The favorable isovalent dopant is the Ge4+ at the Ti site, which may alter the mechanical property of this material. The electronic structures of the favorable dopants are analyzed using density functional theory (DFT) calculations.

DFT interpretations for cycloadditions of an electron deficient C-aryl-N-phenyl nitrone

2014 ◽  
Vol 13 (01) ◽  
pp. 1450007 ◽  
Author(s):  
Nivedita Acharjee
Keyword(s):  
Density Functional ◽  
Transition States ◽  
Density Functional Theory Calculations ◽  
Basis Set ◽  
Dipolar Cycloaddition ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Reaction Channels ◽  
Calculated Activation Energy ◽  
Calculated Activation

1,3-dipolar cycloaddition reactions of an electron deficient C-aryl-N-phenyl nitrone to benzylidene derivatives (with different electrophilicities) have been analyzed by density functional theory calculations. The transition states corresponding to the endo and exo approaches along the feasible regioisomeric reaction channels have been located for each cycloaddition. The reactions follow a concerted mechanism with asynchronous transition states. The asynchronicity along the regiochemical reaction modes depends on the β-carbon electrophilicities of the olefins. The regio and stereochemistries predicted from the calculated activation energy barriers (with solvent and higher basis set corrections) of the located transition states are in conformity with the experimental results. The local electrophilicities, softness matching indices and the interaction energies were then calculated to analyze how well these reactivity parameters can interpret the regioselectivities of such reactions. The electronic populations at the reactive sites computed from electrostatic potential-driven atomic charges provided correct and consistent predictions for each theoretical model contrary to the natural orbital based charges.

AB Initio Calculations of Point Defects in Silicon

1998 ◽  
Vol 538 ◽  
Author(s):  
Jianjun Xie ◽  
S.P. Chen
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Vacancy Defect ◽  
Functional Theory ◽  
Vacancy Pair ◽  
The Density Functional Theory ◽  
Calculated Activation Energy ◽  
Lattice Distortions ◽  
Calculated Activation ◽  
Good Agreement

AbstractWe use the ab initio plane wave pseudopotential method and the density functional theory (DFT) to study the arsenic(As)-vacancy interactions in silicon. The detailed lattice distortions surrounding the As-vacancy defect and the energetics of As-vacancy reaction around the six-fold ring are investigated. We find that the As displaces its neighboring silicon atoms outward while the vacancy attracts its neighboring atoms inward. The binding energy and the formation energy of an As-vacancy pair are 1.21 eV and 2.37 eV, respectively. Once the vacancy and As binds together, the highest migration barrier for the whole complex is 1.19 eV, which is in good agreement with the experimental measurement of 1.07 eV. The calculated activation energy for the vacancy mediated diffusion of the neutral As in silicon is 3.56 eV. The nature of the binding between As and vacancy is explained from the lattice distortions introduced by the As-vacancy complex.

scholarly journals Studying on the Addition Reaction Mechanism of Ethylene and Butadiene Based on Density Functional Theory

2021 ◽  
Author(s):  
Kangning Li ◽  
Wei-lin Ma ◽  
Wen-li Xie
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Density Functional ◽  
Addition Reaction ◽  
Exothermic Reaction ◽  
Functional Theory ◽  
Principle Calculation ◽  
First Principle Calculation ◽  
Calculated Activation Energy ◽  
Calculated Activation

Abstract According to the first principle calculation, the addition reaction mechanism of ethylene and butadiene is determined. The reactant, transition state (TS) and product of this addition reaction are confirmed by optimization calculation and frequency analysis. To verify the correctness of the reaction process, we also calculated the reaction path. Result demonstrates that the addition reaction of ethylene and butadiene is an exothermic reaction. Charge transfer is used to explain this novel reaction. The activation energy of the addition reaction of ethylene and butadiene is 0.83 eV, and the heat release of the whole reaction is 2.01 eV. The molecular structure, charge distribution and energy of butadiene and ethylene are investigated at the molecular level. The calculated activation energy is helpful for understanding the cyclic addition reaction of butadiene and ethylene, providing theoretical guidance for experiments and deepening people's understanding of this reaction.

scholarly journals Comparative Study on Electronic Structure and Optical Properties of α-Fe2O3, Ag/α-Fe2O3 and S/α-Fe2O3

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 424
Author(s):  
Cuihua Zhao ◽  
Baishi Li ◽  
Xi Zhou ◽  
Jianhua Chen ◽  
Hongqun Tang
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Electronic Structures ◽  
Density Functional ◽  
Peak Strength ◽  
Visible Range ◽  
High Symmetry ◽  
Functional Theory ◽  
Optical Absorption Peak ◽  
Calculation Results

The electronic structures and optical properties of pure, Ag-doped and S-doped α-Fe2O3 were studied using density functional theory (DFT). The calculation results show that the structure of α-Fe2O3 crystal changes after Ag and S doping, which leads to the different points of the high symmetry of Ag-doped and S-doped α-Fe2O3 with that of pure α-Fe2O3 in the energy band, as well as different Brillouin paths. In addition, the band gap of α-Fe2O3 becomes smaller after Ag and S doping, and the optical absorption peak shifts slightly toward the short wavelength, with the increased peak strength of S/α-Fe2O3 and the decreased peak strength of Ag/α-Fe2O3. However, the optical absorption in the visible range is enhanced after Ag and S doping compared with that of pure α-Fe2O3 when the wavelength is greater than 380 nm, and the optical absorption of S-doped α-Fe2O3 is stronger than that of Ag-doped α-Fe2O3.

scholarly journals Atoms in Highly Symmetric Environments: H in Rhodium and Cobalt Cages, H in an Octahedral Hole in MgO, and Metal Atoms Ca-Zn in C20 Fullerenes

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1281
Author(s):  
Zikri Altun ◽  
Erdi Ata Bleda ◽  
Carl Trindle
Keyword(s):  
Density Functional Theory ◽  
Quantum Theory ◽  
Coordination Number ◽  
Electronic Structures ◽  
Density Functional ◽  
Functional Theory ◽  
Metal Atoms ◽  
Tetragonal Pyramidal ◽  
Non Covalent Interactions ◽  
Covalent Interactions

An atom trapped in a crystal vacancy, a metal cage, or a fullerene might have many immediate neighbors. Then, the familiar concept of valency or even coordination number seems inadequate to describe the environment of that atom. This difficulty in terminology is illustrated here by four systems: H atoms in tetragonal-pyramidal rhodium cages, H atom in an octahedral cobalt cage, H atom in a MgO octahedral hole, and metal atoms in C20 fullerenes. Density functional theory defines structure and energetics for the systems. Interactions of the atom with its container are characterized by the quantum theory of atoms in molecules (QTAIM) and the theory of non-covalent interactions (NCI). We establish that H atoms in H2Rh13(CO)243− trianion cannot be considered pentavalent, H atom in HCo6(CO)151− anion cannot be considered hexavalent, and H atom in MgO cannot be considered hexavalent. Instead, one should consider the H atom to be set in an environmental field defined by its 5, 6, and 6 neighbors; with interactions described by QTAIM. This point is further illustrated by the electronic structures and QTAIM parameters of M@C20, M=Ca to Zn. The analysis describes the systematic deformation and restoration of the symmetric fullerene in that series.

scholarly journals Ab Initio Study of Martensitic Transformation in NiTiPt High Temperature Shape Memory Alloys

2021 ◽  
Vol 11 (15) ◽  
pp. 6878
Author(s):  
Xiaolan Yang ◽  
Jiaxiang Shang
Keyword(s):  
Phase Transition ◽  
Martensitic Transformation ◽  
Electronic Structures ◽  
Density Functional ◽  
Martensite Phase ◽  
Computational Results ◽  
Ab Initio Study ◽  
Functional Theory ◽  
Phase Transition Temperatures ◽  
Martensite Structure

The crystal structures and martensitic transformation of Ti50Ni50−xPtx alloys (x = 0, 6.25, 8.33, 10.42, 12.5, 18.75, 25) were studied by means of density functional theory (DFT). The computational results indicate that the lattice parameters of Ti-Ni-Pt alloys continuously increase with increasing the Pt content. It is found that at ≤ 12.5 at.% Pt, the martensite structure is monoclinic B19′ phase, and the energy differences between parent and martensite phases (ΔE) decrease slightly with a minimum observed at 6.25 at.% Pt. However, when the Pt content is increased to around 15 at.%, the most stable martensite phase is the orthorhombic B19 structure, and the ΔE increases sharply with Pt concentration. It was found that the phase transition temperatures are closely related to the energy differences ΔE between parent and martensite phases. The electronic structures of martensite B19 and B19′ phases are also discussed.

The Quantum Length Dependence of Conductance in Molecular Device: An Ab Initio Study

2010 ◽  
Vol 663-665 ◽  
pp. 519-522
Author(s):  
Cai Juan Xia ◽  
Han Chen Liu ◽  
Ying Tang Zhang
Keyword(s):  
Electronic Transport ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Molecular Device ◽  
Functional Theory ◽  
Length Dependence ◽  
Molecular Conductance ◽  
Homo Lumo ◽  
Molecular Compounds

By Applying Nonequilibrium Green’s Function Formalism Combined First-Principles Density Functional Theory, we Investigate the Electronic Transport Properties of Thiophene and Furan Molecules with Different Quantum Length. the Influence of HOMO-LUMO Gaps and the Spatial Distributions of Molecular Orbitals on the Electronic Transport through the Molecular Device Are Discussed in Detail. the Results Show that the Transport Behaviors Are Determined by the Distinct Electronic Structures of the Molecular Compounds. the Length Dependence of Molecular Conductance Exhibits its Diversity for Different Molecules.

Electronic structure of the thermoelectric materials PbTe and AgPb18SbTe20 from first-principles calculations

2010 ◽  
Vol 25 (6) ◽  
pp. 1030-1036 ◽  
Author(s):  
Pengxian Lu ◽  
Zigang Shen ◽  
Xing Hu
Keyword(s):  
Band Structure ◽  
Thermoelectric Properties ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Partial Density ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Scanning Transmission ◽  
Linearized Augmented Plane Wave

To investigate the effects of substituting Ag and Sb for Pb on the thermoelectric properties of PbTe, the electronic structures of PbTe and AgPb18SbTe20 were calculated by using the linearized augmented plane wave based on the density-functional theory of the first principles. By comparing the differences in the band structure, the partial density of states (PDOS), the scanning transmission microscope, and the electron density difference for PbTe and AgPb18SbTe20, we explained the reason from the aspect of electronic structures why the thermoelectric properties of AgPb18SbTe20 could be improved significantly. Our results suggest that the excellent thermoelectric properties of AgPb18SbTe20 should be attributed in part to the narrowing of its band gap, band structure anisotropy, the much extrema and large DOS near Fermi energy, as well as the large effective mass of electrons. Moreover, the complex bonding behaviors for which the strong bonds and the weak bonds are coexisted, and the electrovalence and covalence of Pb–Te bond are mixed should also play an important role in the enhancement of the thermoelectric properties of the AgPb18SbTe20.

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