scholarly journals The Conundrum of Relaxation Volumes in First-Principles Calculations of Charged Defects in UO2

2019 ◽  
Vol 9 (24) ◽  
pp. 5276 ◽  
Author(s):  
Anuj Goyal ◽  
Kiran Mathew ◽  
Richard G. Hennig ◽  
Aleksandr Chernatynskiy ◽  
Christopher R. Stanek ◽  
...  
Keyword(s):  
Density Functional ◽  
Defect Formation ◽  
Charged Defect ◽  
Functional Theory ◽  
Neutral Material ◽  
Defect Reactions ◽  
Neutral Defect ◽  
Charged Defects ◽  
Formation Energies ◽  
Defect Relaxation

The defect relaxation volumes obtained from density-functional theory (DFT) calculations of charged vacancies and interstitials are much larger than their neutral counterparts, seemingly unphysically large. We focus on UO2 as our primary material of interest, but also consider Si and GaAs to reveal the generality of our results. In this work, we investigate the possible reasons for this and revisit the methods that address the calculation of charged defects in periodic DFT. We probe the dependence of the proposed energy corrections to charged defect formation energies on relaxation volumes and find that corrections such as potential alignment remain ambiguous with regards to its contribution to the charged defect relaxation volume. We also investigate the volume for the net neutral defect reactions comprising individual charged defects, and find that the aggregate formation volumes have reasonable magnitudes. This work highlights the issue that, as is well-known for defect formation energies, the defect formation volumes depend on the choice of reservoir. We show that considering the change in volume of the electron reservoir in the formation reaction of the charged defects, analogous to how volumes of atoms are accounted for in defect formation volumes, can renormalize the formation volumes of charged defects such that they are comparable to neutral defects. This approach enables the description of the elastic properties of isolated charged defects within an overall neutral material.

A complete ab initio thermodynamic and kinetic catalogue of the defect chemistry of hematite α-Fe2O3, its cation diffusion, and sample donor dopants

2021 ◽  
Author(s):  
Shehab Shousha ◽  
Sarah Khalil ◽  
Mostafa Youssef
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Defect Formation ◽  
Defect Chemistry ◽  
Cation Diffusion ◽  
Functional Theory ◽  
Migration Barriers ◽  
Hubbard U ◽  
And Migration ◽  
Formation Energies

This paper studies comprehensively the defect chemistry and cation diffusion in α-Fe2O3. Defect formation energies and migration barriers are calculated using density functional theory with a theoretically calibrated Hubbard U...

Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg storage

2013 ◽  
Vol 1540 ◽  
Author(s):  
Fleur Legrain ◽  
Oleksandr I. Malyi ◽  
Teck L. Tan ◽  
Sergei Manzhos
Keyword(s):  
Density Functional ◽  
Nearest Neighbor ◽  
Defect Formation ◽  
Crystalline Silicon ◽  
Computational Study ◽  
Binding Energies ◽  
Functional Theory ◽  
Wide Range ◽  
Insertion Sites ◽  
Formation Energies

ABSTRACTWe show in a theoretical density functional theory study that amorphous Si (a-Si) has more favorable energetics for Mg storage compared to crystalline Si (c-Si). Specifically, Mg and Li insertion is compared in a model a-Si simulation cell. Multiple sites for Mg insertion with a wide range of binding energies are identified. For many sites, Mg defect formation energies are negative, whereas they are positive in c-Si. Moreover, while clustering in c-Si destabilizes the insertion sites (by about 0.1/0.2 eV per atom for nearest-neighbor Li/Mg), it is found to stabilize some of the insertion sites for both Li (by up to 0.27 eV) and Mg (by up to 0.35 eV) in a-Si. This could have significant implications on the performance of Si anodes in Mg batteries.

scholarly journals Ab Initio Study of MgTe Self-Interstitial (Mgi and Tei): A Wide Band Gap Semiconductor

2017 ◽  
Vol 16 ◽  
pp. 47-51
Author(s):  
Emmanuel Igumbor ◽  
Ezekiel Omotoso ◽  
Walter Ernst Meyer
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Defect Formation ◽  
Local Density ◽  
Wide Band ◽  
Shallow Donor ◽  
Generalized Gradient ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Formation Energies

We present results of defect formation energies and charge state thermodynamic transition levels of Mg and Te interstitials in MgTe wurzite structure. We use the generalized gradient approximation and local density approximation functionals in the framework of density functional theory for all calculations. The formation energies of the Mg and Te interstitials in MgTe for both the tetrahedral and hexagonal configurations were obtained. The Mg and Te interstitials in MgTe depending on the functional, introduced transition state levels that are either donor or acceptor within the band gap of the MgTe. The Te interstitial exhibit charge states controlled metastability, negative-U and DX centre properties. The Mg interstitial acts as deep or shallow donor and there is no evidence of acceptor levels found for the Mg interstitial.

Stability of Neutral Silicon Interstitials in 3C- and 4H-SiC: A First-Principles Study

2009 ◽  
Vol 283-286 ◽  
pp. 74-83 ◽  
Author(s):  
Ting Liao ◽  
Guido Roma
Keyword(s):  
Density Functional ◽  
Lattice Distortion ◽  
Defect Formation ◽  
Plane Waves ◽  
Basis Sets ◽  
Functional Theory ◽  
Local Coordination ◽  
Large Lattice ◽  
Similar Formation ◽  
Formation Energies

The structural stability and properties of single silicon interstitials in their neutral state are investigated via ab initio methods in 3C- and 4H-SiC. By carefully checking the convergence with Brillouin Zone (BZ) sampling and supercell size we show that the split interstitial along <110> direction and tetrahedrally coordinated structure have similar formation energies in the cubic polytype. We discuss possible artifacts coming from the well known Density Functional Theory (DFT) underestimation of the band gap, which is particularly relevant for 3C-SiC. For 4H-SiC, the most energetically favorable silicon interstitial is found to be the split interstitial configuration ISisp<110> but situated in the hexagonal layer. The defect formation energies in 4H-SiC are in general larger than those in 3C-SiC, implying that the insertion of silicon interstitial introduces a large lattice distortion to the local coordination environments and affect even the second- or third-nearest neighbors. We also present an extensive comparison between well converged plane waves calculations and SIESTA [1,2] calculations based on localised orbitals basis sets.

DFT study on thermo-elastic properties of Ru2FeZ (Z = Si, Ge, Sn) Heusler alloys

2018 ◽  
Vol 32 (05) ◽  
pp. 1850045 ◽  
Author(s):  
Aneeza Iftikhar ◽  
Afaq Ahmad ◽  
Iftikhar Ahmad ◽  
Muhammad Rizwan
Keyword(s):  
Thermal Stability ◽  
Elastic Properties ◽  
Density Functional ◽  
Heusler Alloys ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Functional Theory ◽  
Formation Energies ◽  
Thermal Stability Of ◽  
Temperature Melting

We studied the thermo-elastic properties of Ru2FeZ (Z[Formula: see text]=[Formula: see text]Si, Ge, Sn) Heusler alloys within the framework of density functional theory. Thermo-elastic properties corresponding to elastic modulus, anisotropy, phase stability, elastic wave velocities, thermal stability, Debye temperature, melting temperature, thermal conductivity and formation energy are calculated. The elastic constants C[Formula: see text] predict the structural and dynamical stabilities while the formation energies show thermal stability of the alloys at 0 K. Pugh’s and Poisson’s ratios display the ductile nature of alloys. All alloys are anisotropic and we also observed that Ru2FeSn is the hardest material than Ru2FeSi and Ru2FeGe. Moreover, longitudinal mode of vibrations are also observed and are maximum along [100], [110] and [111] directions than the transverse mode of vibrations.

scholarly journals Dumbbell configuration of silicon adatom defects on silicene nanoribbons

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Huynh Anh Huy ◽  
Quoc Duy Ho ◽  
Truong Quoc Tuan ◽  
Ong Kim Le ◽  
Nguyen Le Hoai Phuong
Keyword(s):  
Magnetic Properties ◽  
Band Gap ◽  
Density Functional ◽  
Spin Moment ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Electronic And Magnetic Properties ◽  
Spin Degeneracy ◽  
Silicene Nanoribbons ◽  
Formation Energies

AbstractUsing density functional theory (DFT), we performed theoretical investigation on structural, energetic, electronic, and magnetic properties of pure armchair silicene nanoribbons with edges terminated with hydrogen atoms (ASiNRs:H), and the absorptions of silicon (Si) atom(s) on the top of ASiNRs:H. The calculated results show that Si atoms prefer to adsorb on the top site of ASiNRs:H and form the single- and/or di-adatom defects depending on the numbers. Si absorption defect(s) change electronic and magnetic properties of ASiNRs:H. Depending on the adsorption site the band gap of ASiNRs:H can be larger or smaller. The largest band gap of 1 Si atom adsorption is 0.64 eV at site 3, the adsorption of 2 Si atoms has the largest band gap of 0.44 eV at site 1-D, while the adsorption at sites5 and 1-E turn into metallic. The formation energies of Si adsorption show that adatom defects in ASiNRs:H are more preferable than pure ASiNRs:H with silicon atom(s). 1 Si adsorption prefers to be added on the top site of a Si atom and form a single-adatom defect, while Si di-adatom defect has lower formation energy than the single-adatom and the most energetically favorable adsorption is at site 1-F. Si adsorption atoms break spin-degeneracy of ASiNRs:H lead to di-adatom defect at site 1-G has the highest spin moment. Our results suggest new ways to engineer the band gap and magnetic properties silicene materials.

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