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Otsuka, Ryuji

Shimizu, Koji

Watanabe, Satoshi

English

Engineering Conferences International

NEURAL NETWORK-BASED SIMULATION METHOD TO EXAMINE ION BEHAVIORS UNDER ELECTRIC FIELDS: APPLICATION TO ION MIGRATION IN AMORPHOUS Li3PO4  Koji Shimizu, Department of Materials Engineering, The University of Tokyo shimizu@cello.t.u-tokyo.ac.jp Ryuji Otsuka, Department of Materials Engineering, The University of Tokyo Satoshi Watanabe, Department of Materials Engineering, The University of Tokyo   Key Words: Born effective charge, neural network, molecular dynamics, nudged elastic band, Li-ion migration  The understanding of ionic behavior under external electric fields is of significance for the development of processing methods of ceramic materials and energy-related devices using ion transport. While first-principles calculations based on density functional theory (DFT) have been widely employed to investigate the ion transport phenomena, the huge computational costs hinder their applications, especially under external electric fields. Thus, simulation methods, which can accurately predict physical quantities with low computational costs, are necessary.   In this study, we developed a neural network-based model to predict Born effective charge tensors from a given atomic structure. We evaluated forces acting on each ion due to an applied uniform electric field as a product of the Born effective charge and the electric field. In combination with a neural network potential (NNP) method [1], we built a scheme to simulate ion dynamics under external electric fields using the neural network models. Employing amorphous Li3PO4 as a prototype material, we constructed both the Born effective charge predictor and NNP using first-principles calculation data for various atomic configurations. We successfully obtained the well optimized models, where the root-mean-square errors of the Born effective charges, total energies, and forces in the 10% of test dataset were 0.0376 e/atom, 2.91 meV/atom, and 87.9 meV/Å, respectively.  Using the constructed models, we performed molecular dynamics simulations under the uniform electric field of 0.1 V/Å. The mean square displacement values showed that the Li ion motions were enhanced along the direction of the electric field, i.e., ion migration, which seems physically reasonable (cf., Fig. 1). In addition, we found that the Li ion motions perpendicular to the electric field were also grown. We attributed this to the non-negligible external forces arisen from the off-diagonal components of the Born effective charges. These results suggest that the local atomic structure dependent Born effective charge tensor would be a suitable quantity for a detailed analysis of ion behavior under external electric fields.    [1] J. Behler and M. Parrinello, Phys. Rev. Lett. 98, 146401 (2007).  [2] R. Otsuka, M. Hara, K. Shimizu, and S. Watanabe, in preparation.   Figure 1 – Comparison of the calculated mean square displacement of Li ions in Li3PO4 with or without the electric field. 

Neural Network-Based Simulation Method to Examine Ion Behaviors Under Electric Fields: Application to Ion Migration in Amorphous Li3PO4

https://dc.engconfintl.org/cgi/viewcontent.cgi?filename=0&article=1036&context=efe_advancedmaterials_iii&type=additional

Neural Network-Based Simulation Method to Examine Ion Behaviors Under Electric Fields: Application to Ion Migration in Amorphous Li3PO4

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Engineering Conferences International