Modern band theory of disordered alloys

2008 ◽  
pp. 273-298 ◽  
Author(s):  
A. Bansil
Keyword(s):  
Band Theory ◽  
Disordered Alloys

Modern Band Theory of Disordered Alloys: Basic Concepts Including a Discussion of Momentum Densities

1993 ◽  
Vol 48 (1-2) ◽  
pp. 165-179 ◽  
Author(s):  
A. Bansil
Keyword(s):  
First Principles ◽  
Experimental Studies ◽  
Energy Bands ◽  
Disordered System ◽  
Band Theory ◽  
Fermi Surfaces ◽  
Disordered Alloys ◽  
Electron Positron ◽  
Basic Concepts ◽  
Selection Of

Abstract An overview of some of the basic concepts in the modern first-principles band theory of disordered alloys is given. The question of how the notion of Bloch energy bands and Fermi surfaces generalizes to the case of the disordered system, insofar as the average electronic spectrum is concerned, is stressed. The theory is illustrated with examples chosen from the work on binary alloys; a few examples of the very recent studies of disordered phases of the high-Tc superconductors are also included. The application of the alloy theory to obtain electron and electron-positron momentum densities involved in the analysis of Compton scattering and positron annihilation (angular correlation) experiments in alloys is discussed, with a selection of relevant theoretical and experimental studies.

Ab initio band theory approach to electron energy loss near edge structures

1988 ◽  
Vol 46 ◽  
pp. 506-507
Author(s):  
Xudong Weng ◽  
O.F. Sankey ◽  
Peter Rez
Keyword(s):  
Ab Initio ◽  
Local Density ◽  
Interpolation Method ◽  
Atomic Orbital ◽  
Plane Waves ◽  
Large Set ◽  
Theory Approach ◽  
Band Theory ◽  
Atomic Orbitals ◽  
Pseudopotential Calculations

Single electron band structure techniques have been applied successfully to the interpretation of the near edge structures of metals and other materials. Among various band theories, the linear combination of atomic orbital (LCAO) method is especially simple and interpretable. The commonly used empirical LCAO method is mainly an interpolation method, where the energies and wave functions of atomic orbitals are adjusted in order to fit experimental or more accurately determined electron states. To achieve better accuracy, the size of calculation has to be expanded, for example, to include excited states and more-distant-neighboring atoms. This tends to sacrifice the simplicity and interpretability of the method.In this paper. we adopt an ab initio scheme which incorporates the conceptual advantage of the LCAO method with the accuracy of ab initio pseudopotential calculations. The so called pscudo-atomic-orbitals (PAO's), computed from a free atom within the local-density approximation and the pseudopotential approximation, are used as the basis of expansion, replacing the usually very large set of plane waves in the conventional pseudopotential method. These PAO's however, do not consist of a rigorously complete set of orthonormal states.

Unemployment as an indicator of economic security in the employment sector: A regional dimension

2020 ◽  
Vol 16 (4) ◽  
pp. 715-729
Author(s):  
T.N. Savina
Keyword(s):  
Comparative Analysis ◽  
Age Groups ◽  
National Development ◽  
Federal District ◽  
Economic Security ◽  
Employment Policy ◽  
Multivariate Statistical ◽  
Band Theory ◽  
The Republic ◽  
The Impact

Subject. To achieve a high level of economic security is a key priority of national development. Employment reveals one of the most important aspects of social development of the individual that is associated with his or her needs satisfaction in the sphere of employment and is boon to economic security. Objectives. The purpose of the study is to show the impact of unemployment on economic security in employment. Methods. I apply such scientific methods as dialectical, historical and logical unity, structural and functional analysis, traditional techniques of economic analysis and synthesis. The methods of multivariate statistical and comparative analysis serve as a methodological basis of the study. To determine the indicator of unemployment, I use the band theory. Results. I underpin the growing role of employment in ensuring economic security. The paper presents a comprehensive assessment of the unemployment status and a comparative analysis of the indicator in the Republic of Mordovia, the Volga Federal District, and the Russian Federation as a whole. I identify trends in the average duration of unemployment, show the distribution of unemployed by level of education and age groups. Conclusions. The average annual unemployment rate in the Republic of Mordovia is lower than in Russia and the Volga Federal District. The findings may be useful for public authorities to substantiate their employment policy at both macro- and meso-levels, for designing programs and strategies for socio-economic development of regions and the social security doctrine, as well as in practical activities of employment services.

The Chemical Bond Across the Periodic Table: Part 1 – First Row and Simple Metals

2020 ◽  
Author(s):  
Gabriel Freire Sanzovo Fernandes ◽  
Leonardo dos Anjos Cunha ◽  
Francisco Bolivar Correto Machado ◽  
Luiz Ferrão
Keyword(s):  
Physical Chemistry ◽  
Chemical Bond ◽  
Materials Science ◽  
Chemical Elements ◽  
Orbital Theory ◽  
Solid State Physics ◽  
Band Theory ◽  
Van Der Waals Clusters ◽  
Earth Systems ◽  
Chemical Content

<p>Chemical bond plays a central role in the description of the physicochemical properties of molecules and solids and it is essential to several fields in science and engineering, governing the material’s mechanical, electrical, catalytic and optoelectronic properties, among others. Due to this indisputable importance, a proper description of chemical bond is needed, commonly obtained through solving the Schrödinger equation of the system with either molecular orbital theory (molecules) or band theory (solids). However, connecting these seemingly different concepts is not a straightforward task for students and there is a gap in the available textbooks concerning this subject. This work presents a chemical content to be added in the physical chemistry undergraduate courses, in which the framework of molecular orbitals was used to qualitatively explain the standard state of the chemical elements and some properties of the resulting material, such as gas or crystalline solids. Here in Part 1, we were able to show the transition from Van der Waals clusters to metal in alkali and alkaline earth systems. In Part 2 and 3 of this three-part work, the present framework is applied to main group elements and transition metals. The original content discussed here can be adapted and incorporated in undergraduate and graduate physical chemistry and/or materials science textbooks and also serves as a conceptual guide to subsequent disciplines such as quantum chemistry, quantum mechanics and solid-state physics.</p>

Ordered Intermetallic Nanoparticles with High Catalytic Activity Prepared by an Electrochemically Induced Phase Transformation

2019 ◽  
Author(s):  
Du Sun ◽  
yunfei wang ◽  
Kenneth Livi ◽  
chuhong wang ◽  
ruichun luo ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Diffusion Mechanism ◽  
Reduction Reaction ◽  
Atomic Scale ◽  
High Catalytic Activity ◽  
Ambient Conditions ◽  
Magnetic Devices ◽  
Disordered Alloys ◽  
Ordered Intermetallic ◽  
Intermetallic Nanoparticles

<div> <p>The synthesis of alloys with long range atomic scale ordering (ordered intermetallics) is an emerging field of nanochemistry. Ordered intermetallic nanoparticles are useful for a wide variety of applications such as catalysis, superconductors, and magnetic devices. However, the preparation of nanostructured ordered intermetallics is challenging in comparison to disordered alloys, hindering progress in materials development. We report a process for converting colloidally synthesized ordered intermetallic PdBi<sub>2</sub> to ordered intermetallic Pd<sub>3</sub>Bi nanoparticles under ambient conditions by an electrochemically induced phase transition. The low melting point of PdBi<sub>2</sub> corresponds to low vacancy formation energies which enables the facile removal of the Bi from the surface, while simultaneously enabling interdiffusion of the constituent atoms via a vacancy diffusion mechanism under ambient conditions. The resulting phase-converted ordered intermetallic Pd<sub>3</sub>Bi exhibits 11x and 3.5x higher mass activty and high methanol tolerance for the oxygen reduction reaction compared to Pt/C and Pd/C, respectively,which is the highest reported for a Pd-based catalyst, to the best of our knowledge. These results establish a key development in the synthesis of noble metal rich ordered intermetallic phases with high catalytic activity, and sets forth guidelines for the design of ordered intermetallic compounds under ambient conditions.</p> </div>

scholarly journals Computational Complexity Reduction of Neural Networks of Brain Tumor Image Segmentation by Introducing Fermi–Dirac Correction Functions

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 223
Author(s):  
Yen-Ling Tai ◽  
Shin-Jhe Huang ◽  
Chien-Chang Chen ◽  
Henry Horng-Shing Lu
Keyword(s):  
Neural Networks ◽  
Deep Learning ◽  
Computational Complexity ◽  
High Performance ◽  
Low Cost ◽  
Structural Complexity ◽  
Correction Function ◽  
Computational Time ◽  
Learning Methods ◽  
Band Theory

Nowadays, deep learning methods with high structural complexity and flexibility inevitably lean on the computational capability of the hardware. A platform with high-performance GPUs and large amounts of memory could support neural networks having large numbers of layers and kernels. However, naively pursuing high-cost hardware would probably drag the technical development of deep learning methods. In the article, we thus establish a new preprocessing method to reduce the computational complexity of the neural networks. Inspired by the band theory of solids in physics, we map the image space into a noninteraction physical system isomorphically and then treat image voxels as particle-like clusters. Then, we reconstruct the Fermi–Dirac distribution to be a correction function for the normalization of the voxel intensity and as a filter of insignificant cluster components. The filtered clusters at the circumstance can delineate the morphological heterogeneity of the image voxels. We used the BraTS 2019 datasets and the dimensional fusion U-net for the algorithmic validation, and the proposed Fermi–Dirac correction function exhibited comparable performance to other employed preprocessing methods. By comparing to the conventional z-score normalization function and the Gamma correction function, the proposed algorithm can save at least 38% of computational time cost under a low-cost hardware architecture. Even though the correction function of global histogram equalization has the lowest computational time among the employed correction functions, the proposed Fermi–Dirac correction function exhibits better capabilities of image augmentation and segmentation.

scholarly journals Experimental signatures of nodeless multiband superconductivity in a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ single crystal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chanhee Kim ◽  
Dilip Bhoi ◽  
Yeahan Sur ◽  
Byung-Gu Jeon ◽  
Dirk Wulferding ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Zero Magnetic Field ◽  
Anisotropy Ratio ◽  
Strong Temperature Dependence ◽  
Critical Fields ◽  
Band Theory ◽  
Plane Field ◽  
Low Field ◽  
Out Of Plane

AbstractIn order to understand the superconducting gap nature of a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 single crystal with $$T_{c} = 3.13 \text { K}$$ T c = 3.13 K , in-plane thermal conductivity $$\kappa $$ κ , in-plane London penetration depth $$\lambda _{\text {L}}$$ λ L , and the upper critical fields $$H_{c2}$$ H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term $$\kappa _{0}/T$$ κ 0 / T exists and $$\lambda _{\text {L}}$$ λ L follows a power-law $$T^n$$ T n (T: temperature) with n = 2.66 at $$T \le \frac{1}{3}T_c$$ T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of $$\kappa _{0}$$ κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent $$H_{c2}$$ H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near $$T_c$$ T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the $$H_{c2}$$ H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor.

scholarly journals Free Energy of Metals from Quasi-Harmonic Models of Thermal Disorder

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 195
Author(s):  
Pavel A. Korzhavyi ◽  
Jing Zhang
Keyword(s):  
Free Energy ◽  
First Principles ◽  
Density Functional ◽  
Helmholtz Free Energy ◽  
Complex Materials ◽  
Predictive Capability ◽  
Temperature Dependent ◽  
Disordered Alloys ◽  
Thermal Disorder ◽  
Structure Calculations

A simple modeling method to extend first-principles electronic structure calculations to finite temperatures is presented. The method is applicable to crystalline solids exhibiting complex thermal disorder and employs quasi-harmonic models to represent the vibrational and magnetic free energy contributions. The main outcome is the Helmholtz free energy, calculated as a function of volume and temperature, from which the other related thermophysical properties (such as temperature-dependent lattice and elastic constants) can be derived. Our test calculations for Fe, Ni, Ti, and W metals in the paramagnetic state at temperatures of up to 1600 K show that the predictive capability of the quasi-harmonic modeling approach is mainly limited by the electron density functional approximation used and, in the second place, by the neglect of higher-order anharmonic effects. The developed methodology is equally applicable to disordered alloys and ordered compounds and can therefore be useful in modeling realistically complex materials.

scholarly journals Non-Bloch band theory in bosonic Bogoliubov–de Gennes systems

2021 ◽  
Vol 103 (16) ◽  
Author(s):  
Kazuki Yokomizo ◽  
Shuichi Murakami
Keyword(s):  
Band Theory ◽  
Bloch Band
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