物理科学与技术学院物理讲坛（2019年第13-15讲）

报告题目：2DMatPedia: A Library of 2D Materials by Top-Down and Bottom-Up Approaches

报告人：冯元平，教授

单 位：National University of Singapore

报告时间：2019年7月3日 上午 08:00-09:00

报告地点：赛思学术会堂
报告摘要：Two-dimensional (2D) materials have attracted tremendous amount of interest. Their unique properties are expected to lead to new technologies. In an effort of systematic 2D materials discovery, we have been using both the top-down and the bottom-up approaches to generate 2D structures. On one hand, monolayer structures are theoretically exfoliated from layered three-dimensional structures by a topology-based algorithm. On the other hand, new 2D materials are systematically generated by chemical substitution of elements in the top-down 2D compounds by similar elements from the same group in the periodic table. High throughput first-principles calculations are carried out to study their physical properties. This in-house database is publicly available (http://www.2dmatpedia.org/) and provides a good starting point for further material screening, data mining, data analysis and artificial intelligence applications. Our progress in this project will be reported and some preliminary applications, such as bilayer heterostructures for excitonic solar cell applications, of the 2D materials database will be discussed.

报告题目：Exchange and excitation of single magnetic molecules

报告人：武汝前，副教授

单 位：University of California

报告时间：2019年7月3日 上午09:15-10:15

报告地点：赛思学术会堂
报告摘要：Magnetic single atoms and molecules are receiving intensifying research focus because of their potential as the smallest possible memory, spintronic, and qubit elements. I will discuss results of our resent experimental and theoretical studies that demonstrate the quantitative determination of exchange interaction between two molecules in the STM junction, revealing angstrom-scale regions where the quantum states of two magnetic molecules strongly mix. Theoretical analyses of spin-vibron and spin-phonon coupling will also be discussed for extending the coherence time of quantum spin states.

报告题目：Exciton Dynamics in Organic and Perovskite Photovoltaics

报告人：Gang Lv，教授

单 位：California State University Northridge

报告时间：2019年7月3日 上午 10:30-11:30

报告地点：赛思学术会堂
报告摘要：Exciton dynamics is at the heart of emerging photovoltaic technology employing both organic and inorganic perovskite based materials. Time-dependent density functional theory (TDDFT) has become one of the most powerful and versatile tools to probe exciton dynamics in these materials. Unfortunately, TDDFT is computationally demanding and as a result, its application to realistic materials remains exceedingly difficult. In this talk, I will outline our recent progress in developing accurate and efficient TDDFT methods that would allow us to start addressing these challenges. Among them, a subspace TDDFT method is developed which can calculate both excitation energy and excited state forces accurately for systems containing up to a few thousand electrons. Combining the TDDFT methods with non-adiabatic molecular dynamics, one can perform coupled electron-ion and exciton-ion dynamics where phonons are important in electron transitions and excitations. I’ll show how these first-principles methods can be brought upon to examine exciton dynamics such as spontaneous electron-hole separation and charge stripe formation in perovskite solar cells as well as exciton diffusion in disordered semiconductors for organic photovoltaics.