scholarly journals First-Principles Study of Point-Defect Production in Si and SiC

1997 ◽  
Vol 490 ◽  
Author(s):  
W. Windl ◽  
T. J. Lenosky ◽  
J. D. Kress ◽  
A. F. Voter
Keyword(s):  
Point Defect ◽  
First Principles ◽  
Tight Binding ◽  
Threshold Energy ◽  
Finite Size ◽  
Finite Size Effect ◽  
Defect Production ◽  
Empirical Potentials ◽  
Displacement Threshold ◽  
Experimental Values

ABSTRACTWe have calculated the displacement-threshold energy Ed for point-defect production in Si and SiC using empirical potentials, tight-binding, and first-principles methods. We show that—depending on the knock-on direction—64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. We use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of Ed without employing an MD simulation and the use of computationally more demanding first-principles methods. We compare our results for Ed with the available experimental values. Furthermore, we have examined the temperature dependence of Ed for C in SiC and found it to be negligible.

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 Geometries and Electronic States of Divacancy Defect in Finite-Size Hexagonal Graphene Flakes

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Lili Liu ◽  
Shimou Chen
Keyword(s):  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Singlet State ◽  
Tight Binding ◽  
Finite Size ◽  
Electronic States ◽  
Closed Shell ◽  
Graphene Flakes ◽  
Self Consistent

The geometries and electronic properties of divacancies with two kinds of structures were investigated by the first-principles (U) B3LYP/STO-3G and self-consistent-charge density-functional tight-binding (SCC-DFTB) method. Different from the reported understanding of these properties of divacancy in graphene and carbon nanotubes, it was found that the ground state of the divacancy with 585 configurations is closed shell singlet state and much more stable than the 555777 configurations in the smaller graphene flakes, which is preferred to triplet state. But when the sizes of the graphene become larger, the 555777 defects will be more stable. In addition, the spin density properties of the both configurations are studied in this paper.

Atomistic simulation of defect production in β-SiC

1997 ◽  
Vol 504 ◽  
Author(s):  
R. Devanathan ◽  
W. J. Weber ◽  
T. Diaz de la Rubia
Keyword(s):  
First Principles ◽  
Atomistic Simulation ◽  
Defect Formation ◽  
Defect Production ◽  
Displacement Threshold ◽  
Particle Irradiation ◽  
Atomic Interactions ◽  
Dynamics Simulations ◽  
Cubic Silicon Carbide ◽  
Threshold Energies

ABSTRACTThe process of defect formation and the threshold energies for Si and C displacements along various crystallographic directions in cubic silicon carbide (β-SiC) have been examined using molecular dynamics simulations. A combination of Tersoff and first-principles potentials was used to model the inter-atomic interactions. The lowest threshold energies for C and Si displacements were found to be 28 and 36 eV, respectively. These displacement threshold energies show excellent agreement with the results of recent first-principles calculations in SiC and with experimental observations. Simulation of a 10 keV Si cascade yielded values of about 0.1 ps for the cascade lifetime and about 3.5 for the ratio of the number of surviving C defects to Si defects. Anti-site defects were found on both Si and C sublattices. These defects may play an important role in the amorphization of SiC by energetic particle irradiation.

First-principles calculations for Gilbert damping constant at finite temperature

2021 ◽  
Author(s):  
Ryoya Hiramatsu ◽  
Daisuke Miura ◽  
Akimasa SAKUMA
Keyword(s):  
First Principles ◽  
Finite Temperature ◽  
Spin Fluctuation ◽  
Tight Binding ◽  
First Principles Calculation ◽  
Transverse Spin ◽  
Orbital Method ◽  
Correlation Model ◽  
Gilbert Damping ◽  
Experimental Values

Abstract We propose a first-principles calculation method for the Gilbert damping constants α at finite temperatures. α is described by the torque correlation model in which the electronic structure is computed by the tight-binding linear muffin-tin orbital method. We include the finite-temperature effect as the transverse spin fluctuation in the disordered local moment picture within the coherent potential approximation. Applying the present method to bcc-Fe and L10-FePt, we demonstrate these temperature-dependent α. By comparing our calculated results with experimental results, we find the calculated values are less than half of the experimental values, reflecting the characteristics of the torque correlation model.

scholarly journals Influence of temperature on the displacement threshold energy in graphene

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Alexandru Ionut Chirita Mihaila ◽  
Toma Susi ◽  
Jani Kotakoski
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Threshold Energy ◽  
Displacement Threshold ◽  
Transmission Electron ◽  
Structure Of Nanomaterials ◽  
Influence Of Temperature On ◽  
Good Conductor ◽  
Nucleus Scattering ◽  
Low Dimensional

Abstract The atomic structure of nanomaterials is often studied using transmission electron microscopy. In addition to image formation, the energetic electrons impinging on the sample may also cause damage. In a good conductor such as graphene, the damage is limited to the knock-on process caused by elastic electron-nucleus scattering. This process is determined by the kinetic energy an atom needs to be sputtered, i.e. its displacement threshold energy Ed. This is typically assumed to have a fixed value for all electron impacts on equivalent atoms within a crystal. Here we show using density functional tight-binding simulations that the displacement threshold energy is affected by thermal perturbations of atoms from their equilibrium positions. This effect can be accounted for in the estimation of the displacement cross section by replacing the constant threshold energy value with a distribution. Our refined model better describes previous precision measurements of graphene knock-on damage, and should be considered also for other low-dimensional materials.

scholarly journals Point defect Production, Geometry and Stability in Silicon: a Molecular Dynamics Simulation Study

1993 ◽  
Vol 316 ◽  
Author(s):  
M.-J. Caturla ◽  
T. Diaz De La Rubia ◽  
G.H. Gilmer
Keyword(s):  
Molecular Dynamics ◽  
Point Defect ◽  
Threshold Energy ◽  
Orientation Dependence ◽  
Dynamics Simulation ◽  
Recoil Energy ◽  
Defect Production ◽  
Production Threshold ◽  
Computer Simulation Studies ◽  
Weber Potential

ABSTRACTWe present results of molecular dynamics computer simulation studies of the threshold energy for point defect production in silicon. We employ computational cells with 8000 atoms at ambient temperature of 10 K that interact via the Stillinger-Weber potential. Our simulations address the orientation dependence of the defect production threshold as well as the structure and stability of the resulting vacancy-interstitial pairs. Near the <111> directions, a vacancy-tetrahedral-interstitial pair is produced for 25 eV recoils. However, at 30 eV recoil energy, the resulting interstitial is found to be the <110> split dumbbell configuration. This Frenkel pair configuration is lower in energy than the former by 1.2 eV. Moreover, upon warming of the sample from 10 K the tetrahedral interstitial converts to a <110> split before finally recombining with the vacancy. Along <100> directions, a vacancy-<110> split interstitial configuration is found at the threshold energy of 22 eV. Near <110> directions, a wide variety of closed replacement chains are found to occur for recoil energies up to 45 eV. At 45 eV, the low energy vacancy-<110> split configuration is found. At 300 K, the results are similar. We provide details on the atomic structure and relaxations near these defects as well as on their mobilities.

Anisotropy of damage productions in electron irradiated molybdenum

1978 ◽  
Vol 36 (1) ◽  
pp. 354-355
Author(s):  
K. Izui ◽  
S. Furuno ◽  
H. Otsu ◽  
T. Nishida ◽  
H. Maeta
Keyword(s):  
Electron Flux ◽  
Threshold Energy ◽  
High Energy ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Displacement Threshold ◽  
The Mean ◽  
Channeling Effect ◽  
Different Origins ◽  
Threshold Energies

Anisotropy of damage productions in crystals due to high energy electron bombardment are caused from two different origins. One is an anisotropic displacement threshold energy, and the other is an anisotropic distribution of electron flux near the atomic rows in crystals due to the electron channeling effect. By the n-beam dynamical calculations for germanium and molybdenum we have shown that electron flux at the atomic positions are from ∽4 to ∽7 times larger than the mean incident flux for the principal zone axis directions of incident 1 MeV electron beams, and concluded that such a locally increased electron flux results in an enhanced damage production. The present paper reports the experimental evidence for the enhanced damage production due to the locally increased electron flux and also the results of measurements of the displacement threshold energies for the <100>,<110> and <111> directions in molybdenum crystals by using a high voltage electron microscope.

scholarly journals Horizon radiation reaction forces

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Walter D. Goldberger ◽  
Ira Z. Rothstein
Keyword(s):  
Black Hole ◽  
Equations Of Motion ◽  
Finite Size ◽  
Radiation Reaction ◽  
Effective Field ◽  
Compact Objects ◽  
Finite Size Effect ◽  
Binary Black Holes ◽  
Dissipative Effects ◽  
Reaction Forces

Abstract Using Effective Field Theory (EFT) methods, we compute the effects of horizon dissipation on the gravitational interactions of relativistic binary black hole systems. We assume that the dynamics is perturbative, i.e it admits an expansion in powers of Newton’s constant (post-Minkowskian, or PM, approximation). As applications, we compute corrections to the scattering angle in a black hole collision due to dissipative effects to leading PM order, as well as the post-Newtonian (PN) corrections to the equations of motion of binary black holes in non-relativistic orbits, which represents the leading order finite size effect in the equations of motion. The methods developed here are also applicable to the case of more general compact objects, eg. neutron stars, where the magnitude of the dissipative effects depends on non-gravitational physics (e.g, the equation of state for nuclear matter).

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