scholarly journals Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

2008 ◽  
Vol 23 (10) ◽  
pp. 2757-2773 ◽  
Author(s):  
A. Ramasubramaniam ◽  
M. Itakura ◽  
M. Ortiz ◽  
E.A. Carter
Keyword(s):  
Monte Carlo ◽  
Density Functional ◽  
Hydrogen Diffusion ◽  
Kinetic Monte Carlo ◽  
Computational Cost ◽  
Bulk Diffusion ◽  
Density Functional Theory Calculations ◽  
Atomic Scale ◽  
Energy Barriers ◽  
Eam Potential

We present an off-lattice, on-the-fly kinetic Monte Carlo (KMC) model for simulating stress-assisted diffusion and trapping of hydrogen by crystalline defects in iron. Given an embedded atom (EAM) potential as input, energy barriers for diffusion are ascertained on the fly from the local environments of H atoms. To reduce computational cost, on-the-fly calculations are supplemented with precomputed strain-dependent energy barriers in defect-free parts of the crystal. These precomputed barriers, obtained with high-accuracy density functional theory calculations, are used to ascertain the veracity of the EAM barriers and correct them when necessary. Examples of bulk diffusion in crystals containing a screw dipole and vacancies are presented. Effective diffusivities obtained from KMC simulations are found to be in good agreement with theory. Our model provides an avenue for simulating the interaction of hydrogen with cracks, dislocations, grain boundaries, and other lattice defects, over extended time scales, albeit at atomistic length scales.

scholarly journals The complementary graphene growth and etching revealed by large-scale kinetic Monte Carlo simulation

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Xiao Kong ◽  
Jianing Zhuang ◽  
Liyan Zhu ◽  
Feng Ding
Keyword(s):  
Monte Carlo ◽  
Large Scale ◽  
2D Materials ◽  
Kinetic Monte Carlo ◽  
Computational Cost ◽  
Atomic Scale ◽  
Graphene Growth ◽  
Graphene Island ◽  
Atomic Simulations ◽  
Hole Growth

AbstractTo fully understand the kinetics of graphene growth, large-scale atomic simulations of graphene islands evolution up to macro sizes (i.e., graphene islands of a few micrometers or with billions of carbon atoms) during growth and etching is essential, but remains a great challenge. In this paper, we developed a low computational cost large-scale kinetic Monte Carlo (KMC) algorithm, which includes all possible events of carbon attachments and detachments on various edge sites of graphene islands. Such a method allows us to simulate the evolution of graphene islands with sizes up to tens of micrometers during either growth or etching with a single CPU core. With this approach and the carefully fitted parameters, we have reproduced the experimentally observed evolution of graphene islands during both growth or etching on Pt(111) surface, and revealed more atomic details of graphene growth and etching. Based on the atomic simulations, we discovered a complementary relationship of graphene growth and etching—the route of graphene island shape evolution during growth is exactly the same as that of the etching of a hole in graphene and that of graphene island etching is exactly same as that of hole growth. The complementary relation brings us a basic principle to understand the growth and etching of graphene, and other 2D materials from atomic scale to macro size and the KMC algorithm is expected to be further developed into a standard simulation package for investigating the growth mechanism of 2D materials on various substrates.

Atomic Scale Modeling of ZrO2 and HfO2 Atomic Layer Deposition on Silicon: Linking Density Functional Theory and Kinetic Monte Carlo

2003 ◽  
Vol 786 ◽  
Author(s):  
A. Estève ◽  
L. Jeloaica ◽  
G. Mazaleyrat ◽  
A. Dkhissi ◽  
M. Djafari Rouhani ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Atomic Layer Deposition ◽  
Density Functional ◽  
Kinetic Monte Carlo ◽  
Atomic Layer ◽  
Atomic Scale ◽  
Reaction Pathways ◽  
Quantum Calculations ◽  
Ongoing Research ◽  
Layer Deposition

ABSTRACTThe present paper establishes some required elements from both Quantum calculations and Kinetic Monte Carlo Modeling to perform full atomic scale simulations of Zirconia and Hafnia Atomic Layer Deposition (ALD) on Silicon technology process. In this view, we present quantum cluster calculations that investigate reaction pathways being part of the chemical reactions taking place at the different stages of the ALD growth. In particular, we detail ongoing research effort on the hydrolysis of adsorbed HfCl3 and ZrCl3 on ultra-thin SiO2. At very low water dose, the hydrolysis appears to be un-favourable. The complete reaction pathways with their associated activation barrier are detailed. We then show that actual available mechanisms emanating from quantum calculations are not sufficient to give a coherent picture of the layer structuring through a Kinetic Monte Carlo technique with the hope of giving new directions for further quantum studies.

Magnetic Phase Diagram of Transition Metal Doped ZnO from Density Functional Theory Calculations and Monte Carlo Simulations

2010 ◽  
Vol 1260 ◽  
Author(s):  
Sanjeev K. Nayak ◽  
Heike C. Herper ◽  
Peter Entel
Keyword(s):  
Monte Carlo ◽  
Curie Temperature ◽  
Monte Carlo Simulations ◽  
Ab Initio ◽  
Density Functional ◽  
Magnetic Phase Diagram ◽  
Density Functional Theory Calculations ◽  
Antiferromagnetic Coupling ◽  
Doped Zno ◽  
Co Concentrations

AbstractTransition metals doped ZnO are possible candidates for multiferroics. Here, we have investigated the evolution of ferromagnetism due to Co dopants. The magnetic properties have been studied for Co concentrations from 0 to 100% by using ab-initio methods, i.e., KKR Green's function techniques. In order to estimate the Curie temperature we have performed Monte Carlo simulations with ab-initio calculated exchange parameters.From our calculations the onset of ferromagnetism occurs between 5 to 20% of Co depending on the numerical details of KKR method used. For Co concentrations larger than 50% the system is dominated by antiferromagnetic coupling and no Curie temperature can be obtained.

scholarly journals Migration of Zeolite-Encapsulated Pt and Au Under Reducing Atmospheres

2021 ◽  
Author(s):  
Dianwei Hou ◽  
Christopher Heard
Keyword(s):  
Monte Carlo ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Noble Metals ◽  
Kinetic Monte Carlo ◽  
Pore System ◽  
Kinetic Monte Carlo Simulations ◽  
Zeolite Lta ◽  
Metal Migration ◽  
Energy Surfaces

Unbiased density functional global optimisation calculations, followed by kinetic Monte Carlo simulations are used to enumerate the potential energy surfaces for migration of noble metals Pt and Au inside the pore system of siliceous zeolite LTA. The effects of reducing adsorbates CO and H2 are determined. It is found that the two metals differ significantly in the strength and type of interaction with the framework, with strong, framework breaking interactions between Pt and and the zeolite, but only weak dispersive interactions between Au and the zeolite. Adsorbates are found to dramatically interfere with Pt-framework binding, leading to poorer atom-trapping, enhanced metal migration and faster equilibration.

scholarly journals DFT Studies of Graphene-Functionalised Derivatives of Capecitabine

2017 ◽  
Vol 72 (12) ◽  
pp. 1131-1138 ◽  
Author(s):  
Mehdi Aramideh ◽  
Mahmoud Mirzaei ◽  
Ghadamali Khodarahmi ◽  
Oğuz Gülseren
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Scale ◽  
Phase System ◽  
Molecular Models ◽  
Functional Theory ◽  
Atomic Properties ◽  
Scale Properties ◽  
Derivatives Of

AbstractCancer is one of the major problems for so many people around the world; therefore, dedicating efforts to explore efficient therapeutic methodologies is very important for researchers of life sciences. In this case, nanostructures are expected to be carriers of medicinal compounds for targeted drug design and delivery purposes. Within this work, the graphene (Gr)-functionalised derivatives of capecitabine (CAP), as a representative anticancer, have been studied based on density functional theory calculations. Two different sizes of Gr molecular models have been used for the functionalisation of CAP counterparts, CAP-Gr3 and CAP-Gr5, to explore the effects of Gr-functionalisation on the original properties of CAP. All singular and functionalised molecular models have been optimised and the molecular and atomic scale properties have been evaluated for the optimised structures. Higher formation favourability has been obtained for CAP-Gr5 in comparison with CAP-Gr3 and better structural stability has been obtained in the water-solvated system than the isolated gas-phase system for all models. The CAP-Gr5 model could play a better role of electron transferring in comparison with the CAP-Gr3 model. As a concluding remark, the molecular properties of CAP changed from singular to functionalised models whereas the atomic properties remained almost unchanged, which is expected for a carrier not to use significant perturbations to the original properties of the carried counterpart.

Kinetic Monte Carlo simulations of cascades in Fe alloys

2000 ◽  
Vol 650 ◽  
Author(s):  
C. Domain ◽  
C.S. Becquart ◽  
J.C. van Duysen
Keyword(s):  
Monte Carlo ◽  
Kinetic Monte Carlo ◽  
Md Simulations ◽  
Atom Probe ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Displacement Cascades ◽  
Cu Content ◽  
Primary Damage ◽  
Eam Potential

ABSTRACTThe Pressurized Water Reactor vessel steels are embrittled by neutron irradiation. Among the solute atoms, copper play an important role in the embrittlement and different Cu-rich defects have been experimentally observed to form. We have investigated by Kinetic Monte Carlo (KMC) on rigid lattices the evolution of the primary damage. Since the point defects created by the displacement cascades have very different kinetics, their evolution is tracked in two steps. In a first step, we have studied their recombination in the cascade region and the formation of interstitial clusters using “object diffusion”. The parameters of this model are based on MD simulations, or on first principles calculations. In a second part, we have investigated the subsequent evolution of the primary damage with a model based on a vacancy jump mechanism. These simulations which rely on an adapted EAM potential show the formation of copper rich defects. Some of the potential's predictions that played a key role in the model were checked by ab initio calculations. The defects obtained from these simulations, subsequent to the primary damage created by displacement cascades, exhibit similarities with the ones observed by atom probe. The influence of temperature and Cu content on the final damage was investigated.

scholarly journals Structural, Electronic, and Magnetic Properties of Mn4N Perovskite: Density Functional Theory Calculations and Monte Carlo Study

2019 ◽  
Vol 33 (5) ◽  
pp. 1507-1512 ◽  
Author(s):  
A. Azouaoui ◽  
M. El Haoua ◽  
S. Salmi ◽  
A. El Grini ◽  
N. Benzakour ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Monte Carlo ◽  
Magnetic Properties ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Generalized Gradient ◽  
Critical Temperatures ◽  
Metallic Behavior ◽  
Functional Theory ◽  
Electronic And Magnetic Properties

AbstractIn this paper, we have studied the structural, electronic, and magnetic properties of the cubic perovskite system Mn4N using the first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The obtained data from DFT calculations are used as input data in Monte Carlo simulation with a mixed spin-5/2 and 1 Ising model to calculate the magnetic properties of this compound, such as the total, partial thermal magnetization, and the critical temperatures (TC). The obtained results show that Mn4N has a ferrimagnetic structure with two different sites of Mn in the lattice and presents a metallic behavior. The obtained TC is in good agreement with experimental results.

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