Dalhousie University

报告摘要：

Applying external fields offers an efficient strategy for controlling material behavior. For instance, high pressure can induce phase transitions, while electric fields or voltages can drive ion diffusion and chemical reaction. The atomistic mechanisms underlaying these processes can be explored through computational approaches, providing a foundation to more precise control towards desired outcomes.In this talk, I will present our recent progresses on simulating diffusion, phase transitions, and surface reactions under external fields using first-principles calculations. Three representative examples will be discussed in detail, each illustrating a different level of theoretical treatment of external fields:Small uniform field: Dislocation motion in ZnS entirely driven by electric field. I will discuss how to incorporate the effect of electric field in barrier calculation under the first-order approximation. Density functional theory calculation shows the dislocation is charged and electric field lowers its moving barrier. The same strategy can be adopted for a stress field.

Accounting for electrochemical potential shift:Charge/discharge kinetics in LiNiO2, a Li-ion battery cathode material. High-Ni layered oxide cathodes have high energy density but exhibit profound capacity loss after cycling. The underlying mechanisms have not been well understood, hampering further improvements of these materials. Using LiNiO2 as a model system, our atomistic simulations successfully reproduce the first-cycle irreversible capacity loss at the end of discharge. Also, we find the rate-limiting step switches from diffusion to H2-H3 phase transition at the end of charge. After cycling, the formation of a surface densified phase suppresses the H3 phase nucleation, dramatically impeding the delithiation process when Li content is below 25%. These findings align well with recent experiments.Exact transition state search under constant voltage: surface electrocatalytic reaction. Here, the number of electrons is automatically adjusted to the voltage, and the electric field is not necessarily uniform. Two charge transfer mechanisms of oxygen evolution reaction (OER) on RuO2 are compared.

报告人简介：

Dr. Penghao Xiao is an assistant professor in the Department of Physics and Atmospheric Science at Dalhousie University in Halifax, Nova Scotia, Canada. His research focuses on simulation of materials from first principles, with a particular interest on the kinetic processes that dictates materials’ synthesis, performance, and degradation. Before joining Dalhousie in 2021, Dr. Xiao obtained his Ph.D. from the University of Texas at Austin under the supervision of Dr. Graeme Henkelman. He did his postdoc trainings at Lawrence Berkeley National Laboratory with Dr. Gerbrand Ceder, and then at Lawrence Livermore National Laboratory with Dr. Brandon Wood.

邀请人：程金光

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