學術研究 • ACADEMIC RESEARCH 澳大新語 • 2023 UMAGAZINE 27 66 proposed a computational model for simulating polarons in 2D materials, and a mathematical model for predicting the ground state energy (the lowest energy state that a polaron can occupy in materials) of self-trapped polarons in such materials. Observing Polarons in White Graphene Our research focuses on 2D single-layer materials. They are basically flat structures that are usually only one atom thick, unlike 3D materials with which most people are familiar. In recent years, we have witnessed significant advancements in polaron research in 3D materials, but much remains to be uncovered about 2D materials. Using our new framework, we have for the first time observed a type of Fröhlich hole polarons (a type of polarons with a positively charged hole at its core) in white graphene, a 2D material known scientifically as hexagonal boron nitride (h-BN), and have determined its real-space structure. It has a repeating geometric pattern resembling a honeycomb, as well as unique properties that make it a suitable material for cosmetics, lubrication for satellites and other products. Computer Simulation of 2D Materials Studying polarons in 2D materials often require computer simulation of these materials. Our new computational method can overcome a problem known as the Coulomb divergence. This allows us to accurately describe the geometric details of self-trapped polarons in different 2D materials, and precisely calculate their radius and ground state energy. Furthermore, we have proposed a mathematical model that allows us to calculate whether and how an electron can form a self-trapped polaron in 2D material by considering only three factors, namely the effective mass of the electron, the effective thickness of the 2D material, and the ionic dielectric screening of such a material. Using Impurities to Develop Novel Materials In 2D materials, defects and impurities can significantly affect the behaviour of polarons and can sometimes promote the formation and self-trapping of polarons. We believe that our framework and models may enable physicists to control more precisely the stability, mobility, and properties of polarons in materials, so that they can alter the materials more precisely, by leveraging defects already in the materials, or intentionally introducing impurities to the materials. This will help them more efficiently develop 2D materials with tailored properties. Simulating 100,000 Atoms for Validation We validated this discovery with a simulation of up to 100,000 atoms. This task used thousands of CPU cores of the Lonestar 6 supercomputer at UT Austin. Essential computing power was also provided for this research by the LvLiang Cloud Computing Center in China and the Texas Advanced Computing Center at UT Austin. Our related research article, titled ‘Polarons in Two-dimensional Atomic Crystals’, has been published in Nature Physics. As the quest for smaller and faster devices continues, polarons in 2D materials have emerged as a promising avenue with endless possibilities. That is what propelled us to conduct this research, and what continues to motivate us to develop new theoretical and computational methods. 「學術研究」為投稿欄目，內容僅代表作者個人意見。 Articles in the Academic Research column were submitted by UM scholars. The views expressed are solely those of the author(s). 蕭詠康是澳大應用物理及材料工程研究院的澳大濠江學者，擁有牛津大學計算材料科學博士學位，研究聚焦極子 與電子—聲子相互作用、材料科學的計算方法、凝聚態和電子結構理論，以及二維材料等。 Sio Weng Hong is a UM Macao Fellow in the Institute of Applied Physics and Materials Engineering at UM. He holds a PhD in computational materials science from the University of Oxford. His research interests include polarons and electron-phonon interactions, computational methods for materials science, condensed matter and electronic structure theory, as well as 2D materials.
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