Exploring simulation methods for self-healing oxide films
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0978-GG08-05
Exploring simulation methods for self-healing oxide films Ivan Lazic and Barend Thijsse Materials Science and Engineering, Delft University of Technology, Mekelweg 2, Delft, 2628 CD, Netherlands
ABSTRACT New methods for modeling oxide film growth using MD (molecular dynamics) simulations are explored in order to study the atomic mechanism of the self-healing oxidation phenomenon in metal/oxide systems. A modified MEAM (modified embedded atom method) potential is proposed and extended by a variable charge ionic potential model from the literature, for which the PPPM (particle-particle-particlemesh) is used as Coulomb solver. In this work the first results are reported. The ionic potential model is tested in combination with the PPPM solver. The results are excellent.
INTRODUCTION The surface oxides on aluminum and aluminum alloys can be called “self-healing” in that they quickly re-form after scratching. The initial stage of oxidation is very rapid and is therefore difficult to follow experimentally. Here simulations would be able to extend time scales and resolution to the atomistic domain. However, studying such self-healing phenomena of metal oxides using Molecular Dynamics (MD) simulations requires sophisticated enough interatomic potentials of the undelying metaloxygen systems. The main target of our investigation is Al2O3. For oxides and metal/metal-oxide systems in general, extra difficulties appear because of the presence of ionic bonds, giving rise to long-range Coulomb interactions. Moreover, at interfaces, surfaces and defects, the atomic charges cannot be considered fixed, and models that allow charge transfer should be applied. Finally, aluminum oxide has a relatively open structure, which suggests that angular terms in the interatomic potentials could play an important role. For these reasons we are developing a potential for Al/Al2O3 that combines a chargetransfer potential for the electrostatic interactions with the Modified Embedded Atom Method (MEAM) [1] for the non-electrostatic interactions. Such a potential would also be applicable to the relatively open oxides of e.g. Si and to the mildly ionic III-V and II-VI semiconductors. This paper is a first report on the potential under development and on the implementation of the Coulomb solver. Previous MD work on Al/Al2O3 has been done using MEAM but without considering charges explicitly [2], and using charge transfer ionic potentials but in combination with EAM, which does not includes angular dependencies [3][4]. Here we propose to use the Charge Transfer Ionic Potential (CTIP) published in ref. [4] in combination with a somewhat different version of the MEAM. Unlike previous work, we use the iterative Particle-Particle-Particle-Mesh (PPPM) method as Coulomb solver [5]. PPPM easily adapts to periodic and nonperiodic boundary conditions, and, because of its localized computability, it is convenient for code parallellization. An additional reason is that the computational efficiency of PPPM is ϑ (N log N) while, e.g., for Ewald Summati
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