On the Possibility of Passivation of Si(100) by Adsorption of Group-VI Atoms

1990 ◽  
Vol 193 ◽  
Author(s):  
Efthimios Kaxiras
Keyword(s):  
First Principles ◽  
Relative Strength ◽  
Energy Costs ◽  
First Principles Calculations ◽  
Qualitative Information ◽  
Group Vi ◽  
Covalent Bonds ◽  
Large Dispersion ◽  
Monolayer Coverage ◽  
The Ideal

ABSTRACTThe possibility of passivating the Si(100) surface by adsorption of Group-VI atoms (S and Se) is investigated through first-principles calculations. The structure of the ideal (1×1) configuration with the Si surface dangling bonds saturated by full monolayer coverage is examined in detail. The Group-VI adsorbates form covalent bonds to the substrate with bond-lengths very close to the sums of the covalent radii. The bond-angles are larger than in bulk configurations of the Group-VI elements. The ideal (1×1) configuration gives rise to a surface electronic state with large dispersion spanning the entire band-gap of Si. Deviations from this configuration by in-phase or out-of-phase tilting of the adsorbate atoms result in energy costs which can give qualitative information on the relative strength of adsorbate-adsorbate and adsorbate-substrate interactions.

First-Principles Calculations of Grain Boundary-Surface for Various Grain Boundaries with Different Energies in Aluminum

2007 ◽  
Vol 551-552 ◽  
pp. 331-336 ◽  
Author(s):  
Tokuteru Uesugi ◽  
Y. Inoue ◽  
Yorinobu Takigawa ◽  
Kenji Higashi
Keyword(s):  
Shear Strength ◽  
Grain Boundary ◽  
First Principles ◽  
Boundary Surface ◽  
Grain Boundary Sliding ◽  
Excess Energy ◽  
First Principles Calculations ◽  
Perfect Single Crystal ◽  
Boundary Sliding ◽  
The Ideal

The grain boundary surface is the excess energy of the grain boundary as the lattice on one side of the grain is translated relative to the lattice on the other side of the grain. The maximum in the slope of the grain boundary surface determines the ideal shear strength for the grain boundary sliding. We presented the ideal shear strength for the grain boundary sliding in aluminum Σ3(11 2)[110] tilt grain boundary from the first-principles calculations. The ideal shear strength for the grain boundary sliding was much smaller than the ideal shear strength of a perfect single crystal.

Elastic properties and electronic structure of Mo2FeB2 alloyed with Cr, Ni and Mn by first-principles calculations

2017 ◽  
Vol 31 (12) ◽  
pp. 1750138 ◽  
Author(s):  
Yuan Hua Lin ◽  
Chuang Chuang Tong ◽  
Yong Pan ◽  
Wan Ying Liu ◽  
Ambrish Singh
Keyword(s):  
Electronic Structure ◽  
Elastic Modulus ◽  
Elastic Properties ◽  
First Principles ◽  
Deformation Resistance ◽  
Alloying Elements ◽  
First Principles Calculations ◽  
Volume Deformation ◽  
Covalent Bonds ◽  
G Ratio

In this work, we have applied the first-principles calculations to investigate the structural stability, elastic properties and electronic structure of Mo2FeB2 with alloying elements Cr, Ni and Mn. The calculated cohesive energy shows that Cr, Ni and Mn prefer to occupy the Fe atom of Mo2FeB2. However, only when Mn is doped at the Mo atom of Mo2FeB2, it is converted from dynamic unstable state to stable state. The calculated elastic modulus shows that Mo2FeB2 will have better mechanical properties when alloying elements are at Fe site instead of Mo site. Moreover, Cr addition can improve the volume deformation resistance of Mo2FeB2, Mn addition can improve the shear deformation resistance for Mo2FeB2. The calculated B/G ratio shows that Ni addition can improve the brittleness of borides. Furthermore, the hardness of Mo2FeB2 can be enhanced by adding Cr and Mn element. The calculated electronic structure indicates that the increasing of elastic modulus is attributed to the formation of Cr–B and Mn–B covalent bonds.

The Clustering of Zn6Y9 and its Predominant Role in Long Period Stacking Order Phases in Mg-Zn-Y Alloys: A First-Principles Study

2013 ◽  
Vol 749 ◽  
pp. 569-576 ◽  
Author(s):  
Shang Yi Ma ◽  
Li Min Liu ◽  
Shao Qing Wang
Keyword(s):  
First Principles ◽  
Building Block ◽  
Stacking Fault ◽  
First Principles Calculations ◽  
Predominant Role ◽  
Lpso Phase ◽  
Local Structures ◽  
Long Period ◽  
Stacking Order ◽  
The Ideal

The local structures of Zn and Y in the long period stacking order (LPSO) phase in Mg-Zn-Y system were investigated by first principles calculations in details. The clustering of Zn and Y atoms ranging from single stacking fault layer to four consecutive layers was explicitly demonstrated. The calculations indicate that Zn and Y atoms prefer clustering in the form of Zn6Y9 embedding in ABCA-type building block to the random or ordered arrangements of Zn and Y atoms being enriched in two stacking fault layers. The cluster of Zn6Y9 can be regarded as the ideal stoichiometric component of LPSO and it plays a predominant role in the LPSO phases. The formation of LPSO phases is highly associated with the Zn6Y9 cluster and its derivatives.

scholarly journals Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite

2019 ◽  
Vol 75 (2) ◽  
pp. 260-272 ◽  
Author(s):  
Paul Benjamin Klar ◽  
Iñigo Etxebarria ◽  
Gotzon Madariaga
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Complex Nature ◽  
First Principles Calculations ◽  
Functional Theory ◽  
Modulated Structures ◽  
Total Energies ◽  
The Ideal

The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from first-principles calculations on commensurate structures. The total energies of different configurations allow one to distinguish stable and less stable structure models. The study is based on a series of geometrically optimized superstructures of mullite (Al4+2x Si2−2x O10−x ) derived from the superspace group Pbam(α0½)0ss. Despite the disordered and structurally complex nature of mullite, the calculations on ordered superstructures are very useful for determining the ideal Al/Si ordering in mullite, extracting atomic modulation functions as well as understanding the SiO2–Al2O3 phase diagram. The results are compared with experimentally established models which confirm the validity and utility of the presented method.

scholarly journals Ultimate Mechanical Properties of Forsterite

Minerals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 787 ◽  
Author(s):  
Karine Gouriet ◽  
Philippe Carrez ◽  
Patrick Cordier
Keyword(s):  
Mechanical Properties ◽  
First Principles ◽  
Shear Plane ◽  
Shear Loading ◽  
High Symmetry ◽  
First Principles Calculations ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Homogeneous Strain ◽  
The Ideal

The ultimate mechanical properties, as characterized here by the ideal strengths of Mg2SiO4 forsterite, have been calculated using first-principles calculations and generalized gradient approximation under tensile and shear loading. The ideal tensile strengths (ITS) and ideal shear strengths (ISS) are computed by applying homogeneous strain increments along high-symmetry directions ([100], [010], and [001]) and low index shear plane ((100), (010), and (001)) of the orthorhombic lattice. We show that the ultimate mechanical properties of forsterite are highly anisotropic, with ITS ranging from 12.1 GPa along [010] to 29.3 GPa along [100], and ISS ranging from 5.6 GPa for simple shear deformation along (100) to 11.5 GPa for shear along (010).

scholarly journals Influence of Vacancy Defect on Surface Feature and Adsorption of Cs on GaN(0001) Surface

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Yanjun Ji ◽  
Yujie Du ◽  
Meishan Wang
Keyword(s):  
Work Function ◽  
First Principles ◽  
Density Functional ◽  
Vacancy Defect ◽  
Surface Feature ◽  
First Principles Calculations ◽  
Covalent Bonds ◽  
Functional Theory ◽  
Intact Surface ◽  
Lower Work Function

The effects of Ga and N vacancy defect on the change in surface feature, work function, and characteristic of Cs adsorption on a2×2GaN(0001) surface have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The covalent bonds gain strength for Ga vacancy defect, whereas they grow weak for N vacancy defect. The lower work function is achieved for Ga and N vacancy defect surfaces than intact surface. The most stable position of Cs adatom on Ga vacancy defect surface is at T1site, whereas it is atBGasite on N vacancy defect surface. TheEadsof Cs on GaN(0001) vacancy defect surface increases compared with that of intact surface; this illustrates that the adsorption of Cs on intact surface is more stable.

The pressure dependence of physical properties of (W2/3Ti1/3)3AlC2 and its counterpart W3AlC2 by first-principles calculations

2017 ◽  
Vol 31 (34) ◽  
pp. 1750326 ◽  
Author(s):  
Yefei Li ◽  
Liang Sun ◽  
Jiandong Xing ◽  
Shengqiang Ma ◽  
Qiaoling Zheng ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Hydrostatic Pressure ◽  
First Principles ◽  
Density Functional ◽  
Elastic Anisotropy ◽  
Debye Model ◽  
Mechanical Anisotropy ◽  
Max Phase ◽  
First Principles Calculations ◽  
Covalent Bonds

First-principles calculations based on density functional theory (DFT) were used to investigate the mechanical properties, elastic anisotropy, electronic structure, optical properties and thermodynamic properties of a new quaternary MAX phase (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and its counterpart W[Formula: see text]AlC[Formula: see text] under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] is faster than that of axial shrinkage under hydrostatic pressure. The stress–strain method and Voigt–Reuss–Hill approximation were used to calculate elastic constants and moduli, respectively. These compounds are mechanically stable under hydrostatic pressure. Moreover, the moduli of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] increase with an increase in pressure. The anisotropic indexes and surface constructions of bulk and Young’s moduli were used to illustrate the mechanical anisotropy under hydrostatic pressure. Electronic structure and optical property of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] have also been discussed. The results of Debye temperature reveal that the covalent bonds among atoms in (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] may be stronger than that of W3AlC[Formula: see text]. The heat capacity, [Formula: see text]–[Formula: see text], and thermal expansion coefficient of (W[Formula: see text]Ti[Formula: see text])[Formula: see text]AlC[Formula: see text] and W[Formula: see text]AlC[Formula: see text] were discussed in the ranges of 0–30 GPa and 0–2000 K using quasi-harmonic Debye model considering the phonon effects.

Mechanical Properties and Stability of Body-Centered-Tetragonal C8 at High Pressures

2018 ◽  
Vol 73 (10) ◽  
pp. 939-945
Author(s):  
Chenyang Zhao ◽  
Qun Wei ◽  
Haiyan Yan ◽  
Bing Wei
Keyword(s):  
Mechanical Properties ◽  
First Principles ◽  
Pressure Range ◽  
Superhard Material ◽  
High Pressures ◽  
Elastic Anisotropy ◽  
Acoustic Velocity ◽  
Large Strains ◽  
First Principles Calculations ◽  
The Ideal

AbstractThe structural, mechanical, electronic properties and stability of body-centered-tetragonal C8 (Bct-C8) were determined by using the first-principles calculations. Bct-C8 is identified to be mechanically and dynamically stable at a pressure range from 0 to 100 GPa. The elastic anisotropy, average acoustic velocity and Debye temperature of Bct-C8 at ambient and high pressures were studied. The ideal stresses at large strains of Bct-C8 were examined; the results showed that it would cleave under the tensile strength of 72 GPa or under the shear strength of 70 GPa, indicating that Bct-C8 is a potential superhard material.

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