FERROELECTRIC SWITCHING PATH IN MONODOMAIN RHOMBOHEDRAL BiFeO3 CRYSTAL: A FIRST-PRINCIPLES STUDY

2011 ◽  
Vol 01 (02) ◽  
pp. 179-184 ◽  
Author(s):  
HANG-CHEN DING ◽  
SI-QI SHI ◽  
WEI-HUA TANG ◽  
CHUN-GANG DUAN
Keyword(s):  
First Principles ◽  
Energy Barrier ◽  
Lower Energy ◽  
Density Functional ◽  
Paraelectric Phase ◽  
Magnetic Ordering ◽  
Polarization Direction ◽  
Switching Path ◽  
Abrupt Changes ◽  
Ferroelectric Switching

Based on density-functional calculations, we have studied possible ferroelectric switching path in monodomain single crystal of rhombohedral BiFeO3 , a prototypical multiferroic compound. By carefully studying the behaviors of FeO6 corner-sharing double-tetrahedrons, we find abrupt changes in total energy and oxygen atomic positions, and therefore polarizations, occur in the ferroelectric switching path of rhombohedral BiFeO3 . Detailed analyses suggest that such behavior might be caused by the frustrated magnetic ordering in the paraelectric phase of rhombohedral BiFeO3 , where three O atoms and the Bi atom are in the same plane perpendicular to the polarization direction. This is supported by the fact that the ferroelectric switching for paramagnetic BiFeO3 is smooth and has a much lower energy barrier than that of antiferromagnetic BiFeO3 .

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.

Electronic structure and magnetic ordering in gadolinium-doped AlGaN from LSDA + U calculations

2018 ◽  
Vol 07 (03) ◽  
pp. 1850019 ◽  
Author(s):  
S. Belhachi ◽  
S. Amari ◽  
B. Bouhafs
Keyword(s):  
Density Functional Theory ◽  
Magnetic Properties ◽  
Band Gap ◽  
First Principles ◽  
Density Functional ◽  
Magnetic Ordering ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Indirect Band Gap

We present first-principles calculations of the structural, electronic and magnetic properties of Gd-doped [Formula: see text] based on the density functional theory within [Formula: see text] schemes. It is found that Gd atom favors substituting for Al site. Compared with undoped [Formula: see text], the Gd-doped [Formula: see text] has become an indirect band gap semiconductor of reduced band gap. The magnetic moment [Formula: see text] per molecule mainly comes from Gd ion with little contribution from the Ga, Al and N atoms. It is confirmed that the ferromagnetic configuration is stable for [Formula: see text]. It is found also that there is hybridization between the forbital of the Gd atom and the [Formula: see text] orbital of the N atom.

THE DISSOCIATION AND ISOMERIZATION REACTIONS OF N11 ISOMERS

2003 ◽  
Vol 02 (01) ◽  
pp. 15-22
Author(s):  
QIAN SHU LI ◽  
YONG DONG LIU
Keyword(s):  
Density Functional Theory ◽  
Barrier Height ◽  
Energy Barrier ◽  
Lower Energy ◽  
Density Functional ◽  
Functional Theory ◽  
Barrier Heights ◽  
The Density Functional Theory

The dissociation and isomerization reactions of N 11 isomers, including the two structures 1 and 3 previously studied as well as the three new structures 2, 4, and 5, were investigated by the density functional theory (DFT) at the B3LYP/6-31G(d), B3LYP/6-311G(d), and B3LYP/6-311+G(3df)//B3LYP/6-311G(d) levels of theory. The results indicate that, similar to previous results on N 9 and N 10 isomers, the barrier heights for structures 1 and 2 to lose N 2 are about 10–15 kcal/mol whereas the barrier heights for structures 1–3 to lose N 3 are about 25–30 kcal/mol. Therefore, it seems that N 2 is easier to be eliminated than is N 3 from the relatively larger nitrogen isomers. In addition, for structures 1 and 3, both dissociation and isomerization can occur in the N8–N9 bond, due partly to its character in having an aromatic bond. Moreover, the isomerization is preferred compared with dissociation because of its relatively lower energy barrier height.

Influence of Nd-Doping on Electronic Structure and Optical Properties of ZnO

2014 ◽  
Vol 941-944 ◽  
pp. 658-661
Author(s):  
Lan Li Chen ◽  
Hong Duo Hu ◽  
Zhi Hua Xiong
Keyword(s):  
Optical Properties ◽  
Electronic Structure ◽  
Conduction Band ◽  
First Principles ◽  
Energy Region ◽  
Lower Energy ◽  
Density Functional ◽  
Functional Theory ◽  
Level Shifts ◽  
Lower Energy Region

A detailed first-principles study of electronic structure and optical properties of Nd-doping ZnO with various concentrations of Nd was performed using density functional theory. The results show that the band gap of Nd-doping ZnO slightly widens with the increasing Nd concentration, this is because the conduction band undergoes a greater shift toward the lower-energy region than the valence band, which is agreement with experimental results. Furthermore, in comparison to pure-ZnO, the Fermi level shifts into the conduction band after Nd-doping ZnO. And the calculated result of imaginary part of dielectric function of Nd-doping ZnO shows that there is a sharp peak in the lower-energy region, which is due to the electrons transition between d-d orbital of Nd atom.

Energy Landscape of Displacive Phase Transition of β to ω in Ti-V alloys

MRS Advances ◽  
2017 ◽  
Vol 2 (27) ◽  
pp. 1449-1454 ◽  
Author(s):  
Wei Mei ◽  
Jian Sun
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Ground State ◽  
First Principles ◽  
Energy Barrier ◽  
Density Functional ◽  
Energy Landscape ◽  
Functional Theory ◽  
Ω Phase ◽  
Displacive Phase Transition

ABSTRACTThe ground state properties of pure Ti with α, β and ω structures and of the binary Ti-xV(x=5‒30) at.% alloys with β and ω structures were calculated by first-principles method based on density functional theory, and subsequently the energy landscape of the displacive phase transition of β to ω were determined. The calculated results show that the energy barrier appears for the displacive phase transition of β to ω in Ti-(15‒30) at.% V alloys at 300 K, but does not at 0 K. The energy barriers increase monotonously with increase of the temperature and the V content. These results can explain the formation of athermal ω phase and shear-assisted β to ω transition observed in as-quenched Ti-V base alloys.

First-principles study of the cubic CaHfO3 (001) surface

2016 ◽  
Vol 30 (24) ◽  
pp. 1650168 ◽  
Author(s):  
Kun Yang ◽  
Yanqing He ◽  
Li Yao ◽  
Yi Cheng ◽  
Guiqiu Wang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Dft Calculations ◽  
First Principles ◽  
Electronic Structures ◽  
Lower Energy ◽  
Density Functional ◽  
Functional Theory ◽  
First Principles Study

The geometric and electronic structures of the cubic CaHfO3 (001) surfaces have been studied using first-principles density functional theory (DFT) calculations. Two different terminations, CaO- and HfO2-terminated surfaces, were investigated. It has been found that Ca atom has the largest relaxation for both kinds of terminations, and the surface rumpling of the CaO termination is far more prominent than that of the HfO2-terminated surface. Both the bandgaps of the CaO- and HfO2-terminated surfaces were calculated to be smaller than that of the CaHfO3 bulk. It was also shown that the CaO-terminated surface has a lower energy than the HfO2-terminated surface.

Structural, Electronic and Optical Properties of S-Doped Anatase TiO2

2015 ◽  
Vol 727-728 ◽  
pp. 79-82 ◽  
Author(s):  
Wei Zeng ◽  
Qi Jun Liu ◽  
Zheng Tang Liu
Keyword(s):  
Optical Properties ◽  
Optical Absorption ◽  
Absorption Edge ◽  
First Principles ◽  
Lower Energy ◽  
Density Functional ◽  
Optical Absorption Edge ◽  
Functional Theory ◽  
Electronic And Optical Properties ◽  
Valence Bands

Structural, electronic and optical properties of S-doped anatase TiO2 have been investigated using the first-principles density-functional theory. The band structure and density of states show that the band gap of anatase TiO2 narrows due to the presence of the S-3p energy level in the top of the valence bands. Compared with the optical absorption edge of the undoped anatase TiO2, the optical absorption edge of S-doped anatase TiO2 shifts to a lower energy, which indicates that S-doped anatase TiO2 can be used for visible-light absorption applications.

First-Principles Evaluation of the Potential of Borophene as a Monolayer Transparent Conductor

2017 ◽  
Author(s):  
Lyudmyla Adamska ◽  
Sridhar Sadasivam ◽  
Jonathan J. Foley ◽  
Pierre Darancet ◽  
Sahar Sharifzadeh
Keyword(s):  
First Principles ◽  
Density Functional ◽  
State Of The Art ◽  
Transparent Electrode ◽  
Visible Range ◽  
Two Dimensional ◽  
Transparent Conductor ◽  
Many Body ◽  
Functional Theory ◽  
Many Body Perturbation Theory

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron-phonon and electron-electron interactions, we show that the electrical conductivity is limited by electron-phonon interactions. Our results indicate that both structures are suitable as a transparent electrode.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

uMBD: A Materials-Ready Dispersion Correction that Uniformly Treats Metallic, Ionic, Covalent, and van der Waals Bonding

2019 ◽  
Author(s):  
Minho Kim ◽  
won june kim ◽  
Tim Gould ◽  
Eok Kyun Lee ◽  
Sébastien Lebègue ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Electrode Materials ◽  
Full Range ◽  
Van Der Waals ◽  
Dft Method ◽  
Dispersion Correction ◽  
Computational Overhead ◽  
System A ◽  
Battery Design

<p>Materials design increasingly relies on first-principles calculations for screening important candidates and for understanding quantum mechanisms. Density functional theory (DFT) is by far the most popular first-principles approach due to its efficiency and accuracy. However, to accurately predict structures and thermodynamics, DFT must be paired with a van der Waals (vdW) dispersion correction. Therefore, such corrections have been the subject of intense scrutiny in recent years. Despite significant successes in organic molecules, no existing model can adequately cover the full range of common materials, from metals to ionic solids, hampering the applications of DFT for modern problems such as battery design. Here, we introduce a universally optimized vdW-corrected DFT method that demonstrates an unbiased reliability for predicting molecular, layered, ionic, metallic, and hybrid materials without incurring a large computational overhead. We use our method to accurately predict the intercalation potentials of layered electrode materials of a Li-ion battery system – a problem for which the existing state-of-the-art methods fail. Thus, we envisage broad use of our method in the design of chemo-physical processes of new materials.</p>

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