Vacancy Migration Barrier Energetics and Pathways in Silica

1998 ◽  
Vol 538 ◽  
Author(s):  
L. R. Corrales ◽  
R.M. Van Ginhoven ◽  
J. Song ◽  
H. Jónsson
Keyword(s):  
Point Defect ◽  
Defect Formation ◽  
Vacancy Defect ◽  
Elastic Band ◽  
Simulation Methodology ◽  
Defect Migration ◽  
Migration Pathway ◽  
Empirical Potentials ◽  
Band Method ◽  
Migration Pathways

AbstractA study of vacancy defect migration pathways and energetics in a-quartz is carried out using an empirical simulation methodology that is coupled with the nudged elastic band method. Results from this study indicate that the migration pathway for migration is between adjacent sites. We anticipate the results will guide modifications to empirical potentials for use in the study of point defect formation of more complex systems.

scholarly journals Ab Initio Investigation of Helium Mobility in La2Zr2O7 Pyrochlore

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 667
Author(s):  
Yanxia Lu ◽  
Qing Peng ◽  
Chenguang Liu
Keyword(s):  
Nuclear Waste ◽  
Density Functional ◽  
Minimum Energy ◽  
Elastic Band ◽  
Waste Forms ◽  
Band Method ◽  
And Migration ◽  
High Level ◽  
Migration Pathways ◽  
Nuclear Waste Forms

The α-decay of incorporated actinides continuously produces helium, resulting in helium accumulation and causing security concerns for nuclear waste forms. The helium mobility is a key issue affecting the accumulation and kinetics of helium. The energy barriers and migration pathways of helium in a potential high-level nuclear waste forms, La2Zr2O7 pyrochlore, have been investigated in this work using the climbing image nudged elastic band method with density functional theory. The minimum energy pathway for helium to migrate in La2Zr2O7 is identified as via La–La interstitial sites with a barrier of 0.46 eV. This work may offer a theoretical foundation for further prospective studies of nuclear waste forms.

Kinetics of Frenkel Defect Formation in TiO2 from First Principles

2013 ◽  
Vol 1561 ◽  
Author(s):  
Sergey V. Barabash ◽  
Charlene Chen ◽  
Dipu Pramanik ◽  
Blanka Magyari-Köpe ◽  
Yoshio Nishi
Keyword(s):  
First Principles ◽  
Defect Formation ◽  
Elastic Band ◽  
Unusual Behavior ◽  
Interstitial Position ◽  
Frenkel Defect ◽  
Electrical Stress ◽  
Band Method ◽  
Stress Damage ◽  
Annealing Experiments

ABSTRACTMotivated by the unusual behavior of TiO2 films seen in electrical stress and defect annealing experiments, we studied the energy profile for forming a Frenkel defect in rutile TiO2, using first-principles calculations with a nudged-elastic-band method. We found strongly asymmetric diffusion barriers. The Frenkel pairs with small separation are exceedingly short-lived: the Ti interstitial position nearest to the the Ti vacancy is separated by only a 0.15eV barrier, and the next-nearest interstitial position is dynamically unstable. The formation enthalpies of Frenkel pairs with larger separation gradually vary between 4.2 and 5.0 eV, separated by 0.3-0.4eV barriers along the (001) direction. Contrary to some previous studies, we do not find Frenkel configurations with tetrahedrally bonded Ti interstitials. The very low barriers for Frenkel defect evolution are consistent with the observations from the electrical stress damage annealing experiments.

Exploring the Excited States of Vacancy Defects in Silica

1998 ◽  
Vol 540 ◽  
Author(s):  
J. Song ◽  
L. R. Corrales ◽  
H. Jònsson
Keyword(s):  
Density Functional ◽  
Defect Formation ◽  
Initial Study ◽  
Vacancy Defect ◽  
Dynamics Simulation ◽  
Electronic Excitations ◽  
Defect States ◽  
Functional Theory ◽  
Vacancy Defects ◽  
Simulation Methodology

AbstractA study of vacancy defect formation is carried out using a density functional theory molecular dynamics simulation methodology. The objective is to study the effects of electronic excitations in crystalline and non-crystalline silica polymorphs. We present an initial study focusing on the formation energetics of distinct oxygen vacancy defect states in α-quartz.

Cyclic Slip Localization and Crack Initiation in Crystalline Materials

2014 ◽  
Vol 891-892 ◽  
pp. 452-457 ◽  
Author(s):  
Jaroslav Polák ◽  
Jiří Man
Keyword(s):  
Point Defect ◽  
Defect Formation ◽  
Fatigue Cracks ◽  
Extended Model ◽  
Crystalline Materials ◽  
Defect Migration ◽  
Persistent Slip Bands ◽  
Dislocation Interactions ◽  
Relief Formation ◽  
Cyclic Slip

Cyclic plastic straining in crystalline materials is localized to persistent slip bands (PSBs) and results in formation of persistent slip markings (PSMs) consisting of extrusions and intrusions. Intensive plastic strain in PSBs results in dislocation interactions and formation of point defects. The extended model based on point defect formation, migration and annihilation is presented describing surface relief formation in the form of extrusion-intrusion pairs. Point defect migration and resulting mass transfer is the principle source of cyclic slip irreversibility leading to crack-like defects - intrusions. Fatigue cracks start in the tip of sharp intrusions.

Atomistic Simulation of Nuclear Fuels

2012 ◽  
Vol 1383 ◽  
Author(s):  
Matthias Krack
Keyword(s):  
High Performance ◽  
Program Package ◽  
Quality Level ◽  
Nuclear Fuels ◽  
Elastic Band ◽  
Defect Migration ◽  
Simulation Techniques ◽  
Band Method ◽  
Dynamics Simulations ◽  
Computational Resources

ABSTRACTThe experimental investigation of actinide materials like nuclear fuels is difficult and usually very costly. Therefore a reliable multi-scale modeling of these often hazardous materials starting at the atomistic level is inevitable to gain further insight into this type of materials. The development of new, more advanced simulation methods accompanied by the rapid growth of the available computational resources provided by high-performance computing facilities, allows the modeling of such materials at a new quality level. Also the recent development of the CP2K program package (http://www.cp2k.org) has been partially focused on enabling state-of-the-art simulations of actinide materials using classical potential as well as electronic structure methods. The long-term goal is to perform reliable molecular dynamics simulations for actinide materials including advanced simulation techniques like nudged elastic band or metadynamics simulations. In this work, the CP2K program package and its application to the simulation of defect migration in uranium dioxide (UO2) using the nudged elastic band method is presented.

scholarly journals Paracellular and Transcellular Leukocytes Diapedesis Are Divergent but Interconnected Evolutionary Events

Genes ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 254
Author(s):  
Michel-Edwar Mickael ◽  
Norwin Kubick ◽  
Pavel Klimovich ◽  
Patrick Henckell Flournoy ◽  
Irmina Bieńkowska ◽  
...  
Keyword(s):  
Immune Cell ◽  
Critical Role ◽  
Cellular Polarity ◽  
Endothelial Layer ◽  
Trichoplax Adhaerens ◽  
Migration Pathway ◽  
Two Systems ◽  
Sequence Reconstruction ◽  
Rhoa Protein ◽  
Migration Pathways

Infiltration of the endothelial layer of the blood-brain barrier by leukocytes plays a critical role in health and disease. When passing through the endothelial layer during the diapedesis process lymphocytes can either follow a paracellular route or a transcellular one. There is a debate whether these two processes constitute one mechanism, or they form two evolutionary distinct migration pathways. We used artificial intelligence, phylogenetic analysis, HH search, ancestor sequence reconstruction to investigate further this intriguing question. We found that the two systems share several ancient components, such as RhoA protein that plays a critical role in controlling actin movement in both mechanisms. However, some of the key components differ between these two transmigration processes. CAV1 genes emerged during Trichoplax adhaerens, and it was only reported in transcellular process. Paracellular process is dependent on PECAM1. PECAM1 emerged from FASL5 during Zebrafish divergence. Lastly, both systems employ late divergent genes such as ICAM1 and VECAM1. Taken together, our results suggest that these two systems constitute two different mechanical sensing mechanisms of immune cell infiltrations of the brain, yet these two systems are connected. We postulate that the mechanical properties of the cellular polarity is the main driving force determining the migration pathway. Our analysis indicates that both systems coevolved with immune cells, evolving to a higher level of complexity in association with the evolution of the immune system.

Energetics of point defect formation in Ni3Al

2002 ◽  
Vol 46 (1) ◽  
pp. 37-41 ◽  
Author(s):  
Hannes Schweiger ◽  
Olga Semenova ◽  
Walter Wolf ◽  
Wolfgang Püschl ◽  
Wolfgang Pfeiler ◽  
...  
Keyword(s):  
Point Defect ◽  
Defect Formation

Nudged Elastic Band Method for Molecular Reactions Using Energy-Weighted Springs Combined with Eigenvector Following

2021 ◽  
Author(s):  
Vilhjálmur Ásgeirsson ◽  
Benedikt Orri Birgisson ◽  
Ragnar Bjornsson ◽  
Ute Becker ◽  
Frank Neese ◽  
...  
Keyword(s):  
Elastic Band ◽  
Band Method ◽  
Molecular Reactions

scholarly journals CH4 dissociation on the Pd/Cu(111) surface alloy: A DFT study

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 790-798
Author(s):  
Aykan Akça
Keyword(s):  
Catalytic Activity ◽  
Adsorption Energy ◽  
Lower Cost ◽  
Relative Energy ◽  
Catalyst Design ◽  
Elastic Band ◽  
Efficient Catalyst ◽  
Energy Diagram ◽  
Band Method ◽  
Pure Cu

AbstractThe periodic four-layered model of the pure Cu(111) surface has been considered, and the effect of doping with palladium on CH4 dissociation has been investigated. The most stable adsorption geometries of CHx species (x = 1–4) and H atom on the PdCu(111) and pure Cu(111) surfaces have been obtained. Their computed adsorption energy results on the pure Cu(111) surface have been compared with the previously reported studies. Then, transition state geometries of CH4 dehydrogenation steps on both surfaces were calculated by the climbing image nudged elastic band method. Finally, the relative energy diagram for CH4 complete dehydrogenation has been represented. The results show that the PdCu(111) surface is more favorable than the Cu(111) surface in terms of the activation energies. The addition of Pd atoms to the Cu(111) surface significantly improves the catalytic activity. This knowledge can enable an efficient catalyst design at a lower cost using different strategies.

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