scholarly journals Large Bandgap Topological Insulator in Oxide APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) Perovskite: An Ab Initio Study

2021 ◽  
Vol 11 (3) ◽  
pp. 1143
Author(s):  
Chi-Hsuan Lee ◽  
Jen-Chuan Tung
Keyword(s):  
Elastic Constants ◽  
Density Functional ◽  
Electric Polarization ◽  
Surface Band ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Conduction Channel ◽  
Out Of Plane ◽  
Surface Conduction ◽  
Theory Framework

Under the density functional theory framework, we have calculated the electronic and elastic properties of APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) cubic perovskites. We found that CaPoO3, SrPoO3, BaPoO3, and RaPoO3 are topological insulators (TIs) with very large bandgaps of 0.861, 0.871, 0.820, and 0.810 eV, respectively. The nontrivial band topology together with the Z2 topological number of APoO3 perovskite are investigated. We also theoretically determine the three independent elastic constants C11, C12, and C44 of the APoO3 perovskite. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor are also calculated from the obtained elastic constants. We found that the Debye temperature for the APoO3 perovskite is around 330-370 K. In the bulk APoO3 perovskite, if the center Po atom is shifted 0.09Å away from the center, the induced electric polarization is quite large, being around 0.02 C/m2. In the surface band calculation, we found that both AO and PoO2 surfaces give rise to contributions to the conduction channel. If the Po atom moves both in-plane and out-of-plane, we show that both electric polarization and topologically protect surface conduction states exist in APoO3 perovskite, indicating that these oxide APoO3 perovskites are ferroelectric TIs and might be useful for spintronic applications.

scholarly journals Elastic Properties of Orthorhombic YBa2Cu3O7 under Pressure

Crystals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 497 ◽  
Author(s):  
Cai Chen ◽  
Lili Liu ◽  
Yufeng Wen ◽  
Youchang Jiang ◽  
Liwan Chen
Keyword(s):  
Thermal Conductivity ◽  
Debye Temperature ◽  
Elastic Constants ◽  
Density Functional ◽  
Elastic Anisotropy ◽  
Elastic Stability ◽  
Functional Theory ◽  
Conductivity Increase ◽  
Isotropic Pressure ◽  
The Density Functional Theory

The pressure dependence of the lattice and elastic constants of the orthorhombic YBa 2 Cu 3 O 7 are firstly investigated using the first principles calculations based on the density functional theory. The calculated lattice parameters at 0 GPa are in agreement with the available experimental data. By the elastic stability criteria under isotropic pressure, it is predicted that YBa 2 Cu 3 O 7 with and orthorhombic structure is mechanically stable under pressure up to 100 GPa. On the basis of the elastic constants, Pugh’s modulus ratio, Poisson’s ratio, elastic anisotropy, Debye temperature, and the minimum thermal conductivity of YBa 2 Cu 3 O 7 under pressure up to 100 GPa are further investigated. It is found that its ductility, Debye temperature, and minimum thermal conductivity increase with pressure.

FIRST-PRINCIPLES STUDY OF Ni ADSORPTION ON Mo(110)

2008 ◽  
Vol 15 (05) ◽  
pp. 661-668
Author(s):  
Y. G. ZHOU ◽  
X. T. ZU ◽  
J. L. NIE ◽  
H. Y. XIAO
Keyword(s):  
First Principles ◽  
Energy Barrier ◽  
Density Functional ◽  
Geometric Analysis ◽  
Alloy Layer ◽  
Layer By Layer ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Low Coverage ◽  
Theory Framework

The adsorption of Ni atom on the Mo (110) surface has been studied within the density functional theory framework. It turned out that Ni–Mo surface alloy was formed with Ni atoms substituting Mo atom in the outermost layer. The subsurface site adsorption was found to be not preferred. Geometric analysis showed that the rumpling between substitutional Ni and Mo in the first alloy layer was about 0.108 Å at medium and low coverage (Θ). In addition, the diffusion of Ni on bare and Ni -substitutional Mo (110) surface has been investigated. It was shown that the diffusion energy barrier was reduced as the increase of coverage on bare Mo (110) surface, which supports the switch of growth mode layer-by-layer to Stranski–Krastanov as the function of coverage. Substitutional Ni atom only slightly increases the energy barrier for Ni diffusion on Mo (110) surface.

scholarly journals Optical Properties of DMA-π-DCV Derivatives: A Theoretical Inspection under the DFT Microscope

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Joaquín Calbo
Keyword(s):  
Optical Properties ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Test System ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Donor Acceptor ◽  
Derivatives Of ◽  
Bridge Length ◽  
Theory Framework

The optical properties of a series of donor-acceptor N,N-dimethylaniline-π-dicyanovinylene (DMA-π-DCV) chromophores have been investigated under the density functional theory framework. Focus has been made on the low-lying charge-transfer (CT) electronic transitions for which experimental data is available. The effect of theπ-conjugated bridge length and type was analysed between the families of oligoene and oligoyne derivatives of increasing size. Theoretical calculations demonstrate that the ethylene bridge is a betterπ-communicator and allows for more delocalized frontier molecular orbitals compared to the acetylene spacer. TheΛdiagnostic test allowed rationalization of the orbital spatial overlap in the main CT excitations. The performance of different density functional rungs was assessed in the prediction of the lowest-lying CT electronic transition. Surprisingly, most modern long-range corrected functionals demonstrated to provide among the largest errors, whereas hybrid functionals showed the best performance. Solvatochromism was confirmed in both oligoene and oligoyne compounds. A donor-acceptor-donor triad based on tetrathiafulvalene was utilised as a test system for the prediction of its two CT bands of different nature, energy, and intensity. The hybrid PBE0 (or a similar hybrid analogue) consolidates as the best choice for the prediction of CT excitations in the DMA-π-DCV push-pull family.

scholarly journals First-Principle Studies of the Vibrational Properties of Carbonates under Pressure

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3644
Author(s):  
Yurii N. Zhuravlev ◽  
Victor V. Atuchin
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Low Frequency ◽  
Hybrid Functional ◽  
Functional Theory ◽  
Lattice Constants ◽  
Atomic Displacements ◽  
Carbonate Ion ◽  
The Density Functional Theory ◽  
Out Of Plane

Using the density functional theory with the hybrid functional B3LYP and the basis of localized orbitals of the CRYSTAL17 program code, the dependences of the wavenumbers of normal long-wave ν vibrations on the P(GPa) pressure ν(cm−1) = ν0 + (dv/dP)·P + (d2v/dP2)·P and structural parameters R(Å) (R: a, b, c, RM-O, RC-O): ν(cm−1) = ν0 + (dv/dR) − (R − R0) were calculated. Calculations were made for crystals with the structure of calcite (MgCO3, ZnCO3, CdCO3), dolomite (CaMg(CO3)2, CdMg(CO3)2, CaZn(CO3)2) and aragonite (SrCO3, BaCO3, PbCO3). A comparison with the experimental data showed that the derivatives can be used to determine the P pressures, a, b, c lattice constants and the RM-O metal-oxygen, and the RC-O carbon-oxygen interatomic distances from the known Δν shifts. It was found that, with the increasing pressure, the lattice constants and distances R decrease, and the wavenumbers increase with velocities the more, the higher the ν0 is. The exceptions were individual low-frequency lattice modes and out-of-plane vibrations of the v2-type carbonate ion, for which the dependences are either nonlinear or have negative dv/dP (positive dv/dR) derivatives. The reason for this lies in the properties of chemical bonding and the nature of atomic displacements during these vibrations, which cause a decrease in RM-O and an increase in RC-O.

Study of first principles on anisotropy and elastic constants of YAl3 compound

2020 ◽  
Vol 98 (4) ◽  
pp. 357-363
Author(s):  
Tahsin Özer
Keyword(s):  
Elastic Constants ◽  
First Principles ◽  
Density Functional ◽  
Theoretical Data ◽  
Anisotropic Behavior ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Generalized Gradient Approximation ◽  
The Density Functional Theory ◽  
Quantum Espresso

Using the density functional theory (DFT) calculations, the structural optimization of the YAl3 compound was performed on the generalized gradient approximation (GGA) with quantum ESPRESSO (QE) software. Elastic constants were calculated after the optimization process. Polycrystalline quantities, such as bulk and shear modulus, Young’s modulus, and Poisson’s ratio, were determined using calculated elastic constants. The anisotropy of the compound was studied in detail. As a result of the calculations made, it was observed that the YAl3 compound exhibited mechanically stable structure and anisotropic behavior. In the ht2-YAl3 phase, the effect of pressure on physical properties was investigated in detail. The obtained results were compared with the existing experimental and other theoretical data.

scholarly journals Polyelectrolyte chain at thermal equilibrium: A comparison between the density functional theory framework (DFT) and the molecular dynamic simulations (MD)

2021 ◽  
Author(s):  
Mike J. Edwards
Keyword(s):  
Density Functional Theory ◽  
Molecular Dynamic ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Molecular Dynamic Simulations ◽  
Dynamic Simulations ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Bjerrum Length ◽  
Theory Framework

ABSTRACTBy means of the density functional theory framework (DFT) as well as the molecular dynamic simulations (MD), a polyelectrolyte chain (PE) in the good solvent conditions at thermal equilibrium is studied. The strength of the electrostatic interactions is varied by the Bjerrum length of the solvent. It turns out that average extension of a PE scales with the degree of polymerization, very much similar to a neutral polymer chain in good solvent. Remarkably, the difference between a PE and a neutral chain appears to be solely in the correlations among monomers which are stored in the Virial coefficients. Interestingly, upon increasing the Bjerrum length of solvent, the chain shrinks. This outcome is confirmed by the DFT framework as well as the MD simulations.SIGNIFICANCEThe significance of this study is that it strongly criticizes the idea (already mentioned in T. Kreer, Soft Matter, 12, 3479 (2016)) that the PEs behave similar to a neutral ideal chain. This study could be useful in our understanding of biopolymers.

First-Principles Calculation of Elastic Constants for FeP

2013 ◽  
Vol 321-324 ◽  
pp. 1761-1765 ◽  
Author(s):  
Jian Ying Li ◽  
Jing Zhang ◽  
Qi Zhi Cao ◽  
Yi Fang Ouyang
Keyword(s):  
Elastic Constants ◽  
Density Functional ◽  
Formation Enthalpy ◽  
Density Functional Theory Method ◽  
First Principles Calculation ◽  
Electronic Density ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Theoretical Results ◽  
Good Agreement

The elastic constants of FeP with orthorhombic structure were calculated by using the density-functional theory method. The formation enthalpy, electronic density of states, bulk modulus, and lattice parameters of orthorhombic FeP were also calculated. All of the results are in good agreement with the experimental data and theoretical results available. The results indicate that orthorhombic FeP intermetallic compound is brittleness.

scholarly journals Polyelectrolyte brush bilayer under shear at linear and nonlinear response regimes: A combination of the density functional theory framework and the scaling theory

2021 ◽  
Author(s):  
Mike John Edwards
Keyword(s):  
Density Functional Theory ◽  
Shear Rate ◽  
Friction Coefficient ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Hydrodynamic Interactions ◽  
Functional Theory ◽  
Global Restructuring ◽  
The Density Functional Theory ◽  
Theory Framework

The density functional theory framework and the scaling theory are employed to approach the problem of the Polyelectrolyte brush bilayer under shear. It turns out that, the system at shear rates larger than a critical shear rate undergo a global restructuring during which chains stretch in the shear direction. In the absence of the electrostatic interactions as well as the hydrodynamic interactions, this global restructuring causes a sublinear scaling of the shear stress with the shear rate which makes the shear thinning effect. Nevertheless, in the presence of the hydrodynamic interactions, not only there is no sublinear regime but also a weak superlinear regime which makes a weak shear thickening effect. In the presence of the electrostatic interactions, the stress tensor components change by their second Virial coefficients, however, their shear rate power law are untouched. Nonetheless, the kinetic friction coefficient is independent of the electrostatic interactions. This suggests that the lubrication is not very much different than the neutral bilayers and the electrostatic interactions do not change that. The results of this study offers that maybe nature uses another mechanism to reduce friction coefficient in synovial joint and other biological systems.

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