scholarly journals First Principles Study of Ga₍₂₀₋x₎Alx⁺ Nanoalloys: Structure, Thermodynamics and Phase Diagram

2021 ◽  
Author(s):  
◽  
Udbhav Ojha
Keyword(s):  
Phase Diagram ◽  
First Principles ◽  
Density Functional ◽  
Phase Changes ◽  
Melting Behaviour ◽  
Functional Theory ◽  
Size Dependent ◽  
Chemical Ordering ◽  
Molecular Dynamics Calculations ◽  
Solid Liquid

<p>Nanoalloys (a finite framework of two or more metal atoms) represent a rapidly growing field owing to the possibilities of tuning its properties as desired for various applications. Their properties are size, shape, composition, chemical ordering, and temperature dependent, thereby offering a large playground for varied research motivations. This thesis documents the investigations on how the addition of aluminium affects the cationic gallium clusters, both in terms of geometric & electronic structure and thermodynamics, which have been observed to show greater-than-bulk melting behaviour for small sizes. A specific cluster size of 20 atoms is selected, Ga₍₂₀₋x₎Alx⁺, with the overall intention of creating a phase diagram which is the most reliable way to predict the phase changes in the system. All the first principles (density functional theory) based Born-Oppenheimer molecular dynamics calculations have been performed in the microcanonical ensemble. Melting behaviour is first studied in the pure Al₂₀⁺ clusters and then in three representative clusters of Ga₍₂₀₋x₎Alx⁺ series: Ga₁₉Al⁺, Ga₁₁Al₉⁺ and Ga₃Al₁₇⁺ clusters. We observe that all the three nanoalloy compositions show greater-than-bulk melting behaviour behaviour as well and in Ga₁₉Al⁺, specifically, Al prefers the internal sites, contrary to the previous arguments. We go on to complete the solid-liquid-like melting phase diagram using the calculated information and further propose a model of these greater-than-bulk melting clusters to be components of the corresponding bulk phases, whether metals or alloys, with additional size-dependent contributions added to it.</p>

scholarly journals First Principles Study of Ga₍₂₀₋x₎Alx⁺ Nanoalloys: Structure, Thermodynamics and Phase Diagram

2021 ◽  
Author(s):  
◽  
Udbhav Ojha
Keyword(s):  
Phase Diagram ◽  
First Principles ◽  
Density Functional ◽  
Phase Changes ◽  
Melting Behaviour ◽  
Functional Theory ◽  
Size Dependent ◽  
Chemical Ordering ◽  
Molecular Dynamics Calculations ◽  
Solid Liquid

<p>Nanoalloys (a finite framework of two or more metal atoms) represent a rapidly growing field owing to the possibilities of tuning its properties as desired for various applications. Their properties are size, shape, composition, chemical ordering, and temperature dependent, thereby offering a large playground for varied research motivations. This thesis documents the investigations on how the addition of aluminium affects the cationic gallium clusters, both in terms of geometric & electronic structure and thermodynamics, which have been observed to show greater-than-bulk melting behaviour for small sizes. A specific cluster size of 20 atoms is selected, Ga₍₂₀₋x₎Alx⁺, with the overall intention of creating a phase diagram which is the most reliable way to predict the phase changes in the system. All the first principles (density functional theory) based Born-Oppenheimer molecular dynamics calculations have been performed in the microcanonical ensemble. Melting behaviour is first studied in the pure Al₂₀⁺ clusters and then in three representative clusters of Ga₍₂₀₋x₎Alx⁺ series: Ga₁₉Al⁺, Ga₁₁Al₉⁺ and Ga₃Al₁₇⁺ clusters. We observe that all the three nanoalloy compositions show greater-than-bulk melting behaviour behaviour as well and in Ga₁₉Al⁺, specifically, Al prefers the internal sites, contrary to the previous arguments. We go on to complete the solid-liquid-like melting phase diagram using the calculated information and further propose a model of these greater-than-bulk melting clusters to be components of the corresponding bulk phases, whether metals or alloys, with additional size-dependent contributions added to it.</p>

scholarly journals The stability and electronic and photocatalytic properties of the ZnWO4 (010) surface determined from first-principles and thermodynamic calculations

RSC Advances ◽  
2021 ◽  
Vol 11 (38) ◽  
pp. 23477-23490
Author(s):  
Yonggang Wu ◽  
Jihua Zhang ◽  
Bingwei Long ◽  
Hong Zhang
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Thermodynamic Calculations ◽  
Photocatalytic Properties ◽  
Thermodynamic Approach ◽  
Functional Theory ◽  
Stability Phase Diagram ◽  
The Stability

The ZnWO4 (010) surface termination stability is studied using a density functional theory-based thermodynamic approach. The stability phase diagram shows that O-Zn, DL-W, and DL-Zn terminations of ZnWO4 (010) can be stabilized.

scholarly journals First-Principles Determination of the Polarizabilities of Carbon Tubules as a Function of Length

1994 ◽  
Vol 349 ◽  
Author(s):  
Andrew A. Quong ◽  
Mark R. Pederson
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Valence Electron ◽  
Local Density ◽  
Density Approximation ◽  
Functional Theory ◽  
Size Dependent ◽  
The Density Functional Theory ◽  
Linear And Nonlinear

ABSTRACTWe use the local-density-approximation to the density-functional theory to determine the axial polarizabilities of fullerene tubules as a function of length and winding topologies. Specifically, we present linear polarizabilities for tubules of composition C12H24, C36H24, C40H20 and C60H24. The size-dependent variation in the dipole-coupled gaps between pairs of occupied and unoccupied levels leads to enhancements in the polarizability per valence electron as the length of the tubule increases. The results are compared to recent densityfunctional based calculations of the linear and nonlinear polarizabilities for fullerene and benzene molecules.

scholarly journals Revisiting the zero-temperature phase diagram of stoichiometric SrCoO3 with first-principles methods

2016 ◽  
Vol 18 (44) ◽  
pp. 30686-30695 ◽  
Author(s):  
Pablo Rivero ◽  
Claudio Cazorla
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Temperature Phase ◽  
Zero Temperature ◽  
Functional Theory ◽  
Temperature Phase Diagram ◽  
Content Of Oxygen

By using first-principles methods based on density functional theory we revisited the zero-temperature phase diagram of stoichiometric SrCoO3, a ferromagnetic metallic perovskite that undergoes significant structural, electronic, and magnetic changes as its content of oxygen is decreased.

scholarly journals Силицид Mg-=SUB=-2-=/SUB=-Si под давлением: результаты эволюционного поиска из первых принципов

2020 ◽  
Vol 62 (5) ◽  
pp. 783
Author(s):  
Ю.В. Луняков
Keyword(s):  
Phase Diagram ◽  
First Principles ◽  
Density Functional ◽  
Pressure Range ◽  
Structural Changes ◽  
Structural Phase ◽  
Hexagonal Structure ◽  
Magnesium Silicide ◽  
Monoclinic Structure ◽  
Functional Theory

First-principles Density Functional Theory (DFT) evolutionary searches were carried out for magnesium silicide Mg2Si structures. The well-known hexagonal structure of P63/mmc symmetry is shown to transform to monoclinic С2/m structure under pressure Р~34 GPa. The last one is stable up to pressures P<76 GPa. The monoclinic structure is changed by orhorhombic structure Pmmm, which is stable up to pressures P~235 GPa, then losing to monoclinic structure с симметрией P2/m. The structural changes under the pressures P63/mmc → С2/m → Pmmm → Р2/m are shown at the atomic levels. Structural phase diagram of the bulk silicide Mg2Si at the pressure range 0–240 GPa is constructed.

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 First-Principles Studies on the Structural and Electronic Properties of As Clusters

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1596 ◽  
Author(s):  
Jialin Yan ◽  
Jingjing Xia ◽  
Qinfang Zhang ◽  
Binwen Zhang ◽  
Baolin Wang
Keyword(s):  
Genetic Algorithm ◽  
Density Functional Theory ◽  
Binding Energy ◽  
Electronic Properties ◽  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
Size Dependent ◽  
Structural And Electronic Properties ◽  
Homo Lumo

Based on the genetic algorithm (GA) incorporated with density functional theory (DFT) calculations, the structural and electronic properties of neutral and charged arsenic clusters Asn (n = 2–24) are investigated. The size-dependent physical properties of neutral clusters, such as the binding energy, HOMO-LUMO gap, and second difference of cluster energies, are discussed. The supercluster structures based on the As8 unit and As2 bridge are found to be dominant for the larger cluster Asn (n ≥ 8). Furthermore, the possible geometric structures of As28, As38, and As180 are predicted based on the growth pattern.

Phase diagram of water–methane by first-principles thermodynamics: discovery of MH-IV and MH-V hydrates

2017 ◽  
Vol 19 (24) ◽  
pp. 15996-16002 ◽  
Author(s):  
Xiaoxiao Cao ◽  
Yingying Huang ◽  
Xue Jiang ◽  
Yan Su ◽  
Jijun Zhao
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
Monte Carlo ◽  
Energy Storage ◽  
First Principles ◽  
Methane Hydrate ◽  
Density Functional ◽  
Functional Theory ◽  
Packing Algorithm

We disclose a new dense methane hydrate phases (MH-IV) using the Monte-Carlo packing algorithm and density-functional theory (DFT) optimization, which is superior to previous reported filled ices to apply to energy storage.

First-principles study of the binary intermetallics in the Au–Rb system

2014 ◽  
Vol 28 (14) ◽  
pp. 1450112
Author(s):  
Achraf Benmechri ◽  
Yassine Djaballah ◽  
Ahmed Said Amer ◽  
Aissa Belgacem-Bouzida ◽  
Hichem Bouderba
Keyword(s):  
Phase Diagram ◽  
Density Functional Theory ◽  
Phase Diagrams ◽  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
First Principles Calculations ◽  
Functional Theory ◽  
First Principles Study ◽  
Projector Augmented Wave

First-principles calculations within density functional theory (DFT) with the projector augmented wave (PAW) technique were used to investigate the stabilities of intermetallics in the Au – Rb system at 0 K. Four intermetallics: Au 7 Rb 3, Au 3 Rb 2, Au 5 Rb and AuRb were investigated in their observed experimental structures. The Au 2 Rb compound, reported in the Au – Rb phase diagrams without specifying explicitly its structure, was also investigated by inspecting several hypothetical structures. A suspect compound ( AuRb 2) was also investigated. Results show that: (i) The Au 3 Rb 2 and Au 7 Rb 3 compounds, which were never reported in any Au – Rb phase diagram, are stable at 0 K. (ii) The Au 2 Rb compound is not a ground state for all the tested structures. (iii) Stability of the Au 5 Rb and AuRb compounds was confirmed. (iv) The new compound AuRb 2, not yet reported experimentally, is found mechanically stable at 0 K.

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.

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