Quantum Molecular Dynamics Validation of Nanocarbon Synthesis by High-Temperature Oxidation of Nanoparticles
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Quantum Molecular Dynamics Validation of Nanocarbon Synthesis by High-Temperature Oxidation of Nanoparticles Chunyang Sheng, Kenichi Nomura, Pankaj Rajak, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta Collaboratory for Advanced Computation and Simulations Departments of Chemical Engineering and Materials Science, Physics and Astronomy, and Computer Science University of Southern California, Los Angeles, CA 90089-0242, U.S.A. ABSTRACT This study uses ab initio quantum molecular dynamics (QMD) simulations to validate multimillion-atom reactive molecular dynamics (RMD) simulations, and predicts unexpected condensation of carbon atoms during high-temperature oxidation of silicon-carbide nanoparticles (nSiC). For the validation process, a small nSiC in oxygen environment is chosen to perform QMD simulation. The QMD results provide the number of Si-O and C-O bonds as a function of time. RMD simulation is then performed under the identical condition. The time evolutions of different bonds are compared between the QMD and RMD simulations. We observe the condensation of large number of C-cluster nuclei into larger C clusters in both simulations, thereby validating RMD. Furthermore, we use the QMD simulation results as an input to a multiobjective genetic algorithm to train the RMD force-field parameters. The resulting force field far better reproduces the ground-truth QMD simulation results. INTRODUCTION Silicon carbide (SiC) is widely used in high-temperature and high-power electronic devices that significantly improve the efficiency of power switches in electrical grid [1, 2]. Among numerous advantages, SiC’s ability to form a native oxide layer by thermal oxidation is critical for fabricating metal-oxide-semiconductor devices. SiC is also a key ingredient of thermal protection systems in space vehicles [3], where controlling high-temperature oxidation is critical. Besides its importance in power and space applications, oxidation of SiC, especially that of SiC nanoparticles (nSiC), is attracting great attention both scientifically [4] and technologically [5]. Our recent multimillion-atom reactive molecular dynamics (RMD) simulations of the oxidization of nSiC have shown massive clustering of carbon atoms. These simulations were performed using a scalable parallel implementation of reactive force-field (ReaxFF) molecular dynamics (MD) simulation [6-10] based on spatial decomposition and message passing [11]. The ReaxFF parameters to study high-temperature oxidation of SiC has recently been developed [9]. The ReaxFF parameters have been validated against ab initio and experimental results for the equation of state, oxygen binding energy on SiC, heats of formation of major reactants and reaction products, and activation barriers of key chemical reaction. However, direct validation of the ReaxFF parameters for actual reactions of nSiC at high temperatures remains elusive. To further validate the ReaxFF results on the high-temperature reaction mechanisms based on the above force-field parameters, we performed QMD simulat
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