Influence of Interatomic Potentials in MD Investigation of Ordering in a -SiC
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Influence of Interatomic Potentials in MD Investigation of Ordering in a-SiC Xianglong Yuan and Linn W. Hobbs Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. ABSTRACT Molecular dynamics (MD) simulations of a-SiC using several Tersoff potentials have been performed and their influences on structure ordering were studied. It was found that using different potential cutoffs leads to remarkably different structures. An abrupt cutoff at 2.5 Å greatly increases the chemical ordering of a-SiC by disfavoring the formation of Si-Si bonds. In addition, annealing of SiC cascades embedded in β-SiC was simulated, and the final structures were compared. Again, much stronger topological and chemical ordering was observed in the structure modeled with the 2.5 Å potential cutoff. INTRODUCTION Silicon carbide (SiC) is a promising candidate for blanket material of future nuclear fusion reactors, as well as for semiconductor devices used in severe environments, such as in military aircraft and combat vehicles, power generation, and petrochemical industries [1]. Investigations of irradiation damage in SiC and its recovery are thus of scientific and technological interest. While there have been numerous experimental investigations, recent molecular dynamics (MD) simulations of SiC irradiation cascades [1-6] provide new insights into the irradiation process at the atomic-level. Interatomic potentials are crucial to MD simulation. Study [7] has shown that the Tersoff potential [8] is mere appropriate for SiC modeling than is the Pearson [9] and modified EAM [10] potentials, and recent SiC simulations have mostly used the Tersoff potential. However, the Tersoff potential comes in several versions [8,11,12], with some being preferred over another [16]. Tersoff himself mentions that an abrupt truncation at 2.5 Å is problematic and not appropriate for unconstrained dynamical simulations [11,12] and that the smaller energy of tetrahedral interstitial in Si crystal is an artifact of the cutoff [11]. Moreover, his analysis of an ab initio MD-simulated a-SiC [13] gave a chemical disorder χ of 0.6, which agrees with χ = 0.5 for his a-SiC modeled with a smooth cutoff [12]. On the other hand, the experimental value of χ, or even coordination numbers of Si and C, in a-SiC remain controversial [12,13]. Malerba and Perlado [6] and Gao and Weber [4] still preferred using the 2.5 Å cutoff, as its use results in some defect configurations much closer to ab initio results than with other Tersoff potentials [14]. In this paper, we studied the influence of different Tersoff potentials on MD-simulated aSiC structures and on their chemical and topological order. COMPUTATIONAL DETAILS The molecular dynamic simulations in the present study were performed using the program DLPOLY [15]. A constant volume and temperature NVT ensemble with the Berendsen [16] algorithm was used throughout the study. Targeted temperatures were approached by scaling velocities of all the atoms in the simulation systems.
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