scholarly journals On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

2017 ◽  
Vol 8 ◽  
pp. 85505 ◽  
Author(s):  
Pia Seeberger ◽  
Julien Vidal
Keyword(s):  
Point Defect ◽  
First Principles ◽  
Defect Formation ◽  
Finite Size ◽  
Direct Calculation ◽  
Finite Size Effects ◽  
Numerical Errors ◽  
Silicon Vacancy ◽  
Size Dependent ◽  
Very High

Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and –2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

scholarly journals Nonlocal and Size-Dependent Dielectric Function for Plasmonic Nanoparticles

2019 ◽  
Vol 9 (15) ◽  
pp. 3083
Author(s):  
Kai-Jian Huang ◽  
Shui-Jie Qin ◽  
Zheng-Ping Zhang ◽  
Zhao Ding ◽  
Zhong-Chen Bai
Keyword(s):  
Metallic Nanoparticles ◽  
High Efficiency ◽  
Finite Size ◽  
Plasmonic Nanostructures ◽  
Accurate Analysis ◽  
Finite Size Effects ◽  
Size Dependent ◽  
Quantum Size ◽  
The Impact ◽  
Electron Energy Loss

We develop a theoretical approach to investigate the impact that nonlocal and finite-size effects have on the dielectric response of plasmonic nanostructures. Through simulations, comprehensive comparisons of the electron energy loss spectroscopy (EELS) and the optical performance are discussed for a gold spherical dimer system in terms of different dielectric models. Our study offers a paradigm of high efficiency compatible dielectric theoretical framework for accounting the metallic nanoparticles behavior combining local, nonlocal and size-dependent effects in broader energy and size ranges. The results of accurate analysis and simulation for these effects unveil the weight and the evolution of both surface and bulk plasmons vibrational mechanisms, which are important for further understanding the electrodynamics properties of structures at the nanoscale. Particularly, our method can be extended to other plasmonic nanostructures where quantum-size or strongly interacting effects are likely to play an important role.

scholarly journals PHASE TRANSITION AND FRAGMENT PRODUCTION IN THE LATTICE GAS MODEL

1999 ◽  
Vol 08 (06) ◽  
pp. 527-544 ◽  
Author(s):  
FRANCESCA GULMINELLI ◽  
PHILIPPE CHOMAZ
Keyword(s):  
Phase Transition ◽  
Gas Phase ◽  
Lattice Gas ◽  
Canonical Ensemble ◽  
Finite Size ◽  
Direct Calculation ◽  
Lattice Gas Model ◽  
Finite Size Scaling ◽  
Finite Size Effects ◽  
Fragment Production

The critical behavior of fragment production is studied within a Lattice Gas Model in the canonical ensemble. Finite size effects on the liquid-gas phase transition are analyzed by a direct calculation of the partition function, and it is shown that phase coexistence and phase transition are relevant concepts even for systems of a few tens of particles. Critical exponents are extracted from the behavior of the fragment production yield as a function of temperature by means of a finite size scaling. The result is that in a finite system well defined critical signals can be found at supercritical (Kertész line) as well as subcritical densities inside the coexistence zone.

First-Principles Calculations of Point Defect Formation and Anion Diffusion Mechanisms in the Oxyhydride Ba2ScHO3

2020 ◽  
Author(s):  
Akihide Kuwabara ◽  
Fumitake Takeiri ◽  
Haq Nawaz ◽  
Genki Kobayashi
Keyword(s):  
Point Defect ◽  
First Principles ◽  
Defect Formation ◽  
Diffusion Mechanism ◽  
Layered Perovskite ◽  
First Principles Calculations ◽  
Ion Conductor ◽  
Hydride Ion ◽  
Anion Diffusion ◽  
Hydride Ions

<div>Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing hydrogen. La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub> oxyhydride with a layered perovskite (K<sub>2</sub>NiF<sub>4</sub>-type) structure was discovered as a hydride ion conductor, and it was subsequently reported that Ba<sub>2</sub>ScHO<sub>3</sub> with the same crystal structure is also a hydride ion conductor. The two compounds have different anionic sites occupied by hydride ions. In La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub>, the hydride ions occupy equatorial anion sites, while the hydride ions are located at apical anion sites in Ba<sub>2</sub>ScHO<sub>3</sub>. This suggests that hydride ions diffuse through rock-salt layers in Ba<sub>2</sub>ScHO<sub>3</sub>. However, the specific diffusion mechanism resulting in ionic conductivity of Ba<sub>2</sub>ScHO<sub>3</sub> has not been clarified yet. In the present study, the point defect</div><div>formation energies and anionic conduction mechanisms of Ba<sub>2</sub>ScHO<sub>3</sub> were systematically analyzed using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in Ba<sub>2</sub>ScHO<sub>3</sub> rather than oxide ions. The migration energies of vacancy, interstitial and interstitialcy mechanisms were evaluated, and the activation energies of hydride ionic diffusion mediated by the vacancy and the interstitialcy processes was found to be the lowest.</div>

Effects of tensile strain and finite size on thermal conductivity in monolayer WSe2

2019 ◽  
Vol 21 (1) ◽  
pp. 468-477 ◽  
Author(s):  
Kunpeng Yuan ◽  
Xiaoliang Zhang ◽  
Lin Li ◽  
Dawei Tang
Keyword(s):  
Thermal Conductivity ◽  
Transport Equation ◽  
First Principles ◽  
Tensile Strain ◽  
Lattice Thermal Conductivity ◽  
Boltzmann Transport Equation ◽  
Finite Size ◽  
Boltzmann Transport ◽  
Size Dependent

The strain- and size-dependent lattice thermal conductivity of monolayer WSe2 has been investigated using the first-principles based Boltzmann transport equation.

scholarly journals First-Principles Calculations of Point Defect Formation and Anion Diffusion Mechanisms in the Oxyhydride Ba2ScHO3

2020 ◽  
Author(s):  
Akihide Kuwabara ◽  
Fumitake Takeiri ◽  
Haq Nawaz ◽  
Genki Kobayashi
Keyword(s):  
Point Defect ◽  
First Principles ◽  
Defect Formation ◽  
Diffusion Mechanism ◽  
Layered Perovskite ◽  
First Principles Calculations ◽  
Ion Conductor ◽  
Hydride Ion ◽  
Anion Diffusion ◽  
Hydride Ions

<div>Hydride ion conductors are expected to be a new solid electrolyte for electrochemical devices utilizing hydrogen. La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub> oxyhydride with a layered perovskite (K<sub>2</sub>NiF<sub>4</sub>-type) structure was discovered as a hydride ion conductor, and it was subsequently reported that Ba<sub>2</sub>ScHO<sub>3</sub> with the same crystal structure is also a hydride ion conductor. The two compounds have different anionic sites occupied by hydride ions. In La<sub>2-x-y</sub>Sr<sub>x+y</sub>LiH<sub>1-x+y</sub>O<sub>3-y</sub>, the hydride ions occupy equatorial anion sites, while the hydride ions are located at apical anion sites in Ba<sub>2</sub>ScHO<sub>3</sub>. This suggests that hydride ions diffuse through rock-salt layers in Ba<sub>2</sub>ScHO<sub>3</sub>. However, the specific diffusion mechanism resulting in ionic conductivity of Ba<sub>2</sub>ScHO<sub>3</sub> has not been clarified yet. In the present study, the point defect</div><div>formation energies and anionic conduction mechanisms of Ba<sub>2</sub>ScHO<sub>3</sub> were systematically analyzed using first-principles calculations. As a result, hydride ionic defects tend to form preferentially in Ba<sub>2</sub>ScHO<sub>3</sub> rather than oxide ions. The migration energies of vacancy, interstitial and interstitialcy mechanisms were evaluated, and the activation energies of hydride ionic diffusion mediated by the vacancy and the interstitialcy processes was found to be the lowest.</div>

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