scholarly journals Structure of PtRu/Ru(0001) and AgPd/Pd(111) surface alloys: A kinetic Monte Carlo study

2021 ◽  
Author(s):  
David Mahlberg ◽  
Sung Sakong ◽  
Axel Gross
Keyword(s):  
Monte Carlo ◽  
Density Functional ◽  
Structural Changes ◽  
Kinetic Monte Carlo ◽  
Density Functional Theory Calculation ◽  
Operating Conditions ◽  
Vacancy Diffusion ◽  
Surface Alloys ◽  
Bimetallic Surface ◽  
Catalytically Active

Bimetallic surfaces allow tailoring their catalytic activity by modifying their composition and/or structure. However, under operating conditions, catalytically active bimetallic structures are often not stable and change their morphology which might reduce their functionality. Still, catalytically active structures do not necessarily need to be thermodynamically stable and might also be kinetically stabilized. Here we report kinetic Monte Carlo simulations based on density functional theory calculation to address the meta-stability of surface alloy systems. As structural changes can typically only occur via vacancy diffusion in the surface, we first determine the vacancy diffusion barrier as a function of their bimetallic environment. By determining the temporal evolution of the bimetallic surface alloys as a function of temperature, we analyze the factors underlying the stability and structure of the bimetallic surface alloys.

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.

Diffusion in Ni-Based Single Crystal Superalloys with Density Functional Theory and Kinetic Monte Carlo Method

2016 ◽  
Vol 20 (3) ◽  
pp. 603-618 ◽  
Author(s):  
Min Sun ◽  
Zi Li ◽  
Guo-Zhen Zhu ◽  
Wen-Qing Liu ◽  
Shao-Hua Liu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Monte Carlo ◽  
Transition Rate ◽  
Density Functional ◽  
Diffusion Theory ◽  
Kinetic Monte Carlo ◽  
Functional Theory ◽  
Atom Diffusion ◽  
Time Stepping ◽  
Phase Intermetallic

AbstractIn the paper, we focus on atom diffusion behavior in Ni-based superalloys, which have important applications in the aero-industry. Specifically, the expressions of the key physical parameter – transition rate (jump rate) in the diffusion can be given from the diffusion theory in solids and the kinetic Monte Carlo (KMC) method, respectively. The transition rate controls the diffusion process and is directly related to the energy of vacancy formation and the energy of migration of atom from density functional theory (DFT). Moreover, from the KMC calculations, the diffusion coefficients for Ni and Al atoms in the γ phase (Ni matrix) and the γʹ phase (intermetallic compound Ni3Al) of the superalloy have been obtained. We propose a strategy of time stepping to deal with the multi-time scale issues. In addition, the influence of temperature and Al concentration on diffusion in dilute alloys is also reported.

scholarly journals Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

MRS Advances ◽  
2016 ◽  
Vol 1 (17) ◽  
pp. 1203-1208 ◽  
Author(s):  
Brian S. Good
Keyword(s):  
Monte Carlo ◽  
High Temperature ◽  
Oxygen Diffusion ◽  
Density Functional ◽  
Defect Formation ◽  
Kinetic Monte Carlo ◽  
Interstitial Oxygen ◽  
Temperature Oxidation ◽  
Electron Volt ◽  
Formation Energies

ABSTRACTYtterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the transport of oxygen and water vapor through these coatings to the ceramic substrate is undesirable if high temperature oxidation is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated and interstitial oxygen diffusion in Ytterbium disilicate. Oxygen vacancy and interstitial site energies, vacancy and interstitial formation energies, and migration barrier energies were computed using Density Functional Theory. We have found that, in the case of vacancy-mediated diffusion, many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small. In the case of interstitial diffusion, migration barrier energies are typically around one electron volt, but the interstitial defect formation energies are positive, with the result that the disilicate is unlikely to exhibit experience significant oxygen permeability except at very high temperature.

Mechanisms of Diffusion and Dissociation of E-Centers in Silicon

2005 ◽  
Vol 237-240 ◽  
pp. 1129-1134
Author(s):  
Mariya G. Ganchenkova ◽  
V.A. Borodin ◽  
Risto M. Nieminen
Keyword(s):  
Density Functional Theory ◽  
Monte Carlo ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Density Functional ◽  
Kinetic Monte Carlo ◽  
Binding Energies ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Charge States

In this paper we discuss possible mechanisms of PV annealing in Si. Our approach includes a combination of density functional theory and lattice kinetic Monte-Carlo (LKMC) simulations. The density functional theory is used to find the binding energies and jump barriers for P-V pair at different separations (from one to three interatomic bonds between complex constituents) and in different charge states. The mobility of the complex is simulated by LKMC with event probabilities calculated based on the energies from ab-initio calculations. .

Computational Investigation of Selective MOVPE of AlxGa1-xAs in Presence of Hcl

2001 ◽  
Vol 701 ◽  
Author(s):  
Maria Nemirovskaya ◽  
Carlo Cavallotti ◽  
Klavs Jensen
Keyword(s):  
Fluid Dynamics ◽  
Monte Carlo ◽  
Transition State ◽  
Gas Phase ◽  
Kinetic Monte Carlo ◽  
Monte Carlo Model ◽  
Operating Conditions ◽  
Morphology Evolution ◽  
Computational Investigation ◽  
Dynamics Simulations

ABSTRACTThe deposition of AlGaAs in the presence of HCl was investigated at the macroscopic and mesoscopic scales. Fluid dynamics simulations were first performed in order to study the dependence of the deposition rate on the operating conditions. Unknown gas phase and surface kinetic parameters were estimated by quantum chemistry and transition state computations. The fluxes of all species to the surface were thus computed and provided the input to a kinetic Monte Carlo model used to investigate the morphology evolution of the film.

scholarly journals A Relaxation Time Approximation method for the efficient detection of critical states in reactive trajectories

2020 ◽  
Author(s):  
Nikolaos Ntallis ◽  
Georgios S.E. Antipas
Keyword(s):  
Monte Carlo ◽  
Relaxation Time ◽  
Density Functional ◽  
Kinetic Monte Carlo ◽  
Computationally Efficient ◽  
Time Approximation ◽  
Relaxation Time Approximation ◽  
Efficient Detection ◽  
Reactive Trajectories

We present a bespoke theoretical framework aimed at the computationally efficient Monte Carlo generation of reactive trajectories based on an ab initio potential (Density Functional Theory or higher level of theory), perturbed by a time-dependent force, within the Relaxation Time Approximation (RTA) scope. As a case study, we traced the RTA evolution of Stearic acid adsorbed on a CaCO3 surface, for which we submit an initial set of results on the determination of preferred bonding. Generalization of the RTA method may eventually accommodate kinetic Monte Carlo-based approaches for the analysis of the reactive mesoscale.

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