时间：2021年11月2日（周二） 14:00-15:30

Time：14:00-15:30, Tuesday, November 2nd, 2021

主持人: 西湖大学理学院 吴从军 讲席教授

Host：Prof. Congjun Wu, Chair Professor of School of Science, Westlake University

地点：西湖大学云栖校区4号楼311会议室

Venue：Room 311, Building 4, Yunqi Campus

主讲嘉宾/Speaker：

卢仲毅 教授

Prof. Zhongyi Lu

教授，物理系材料计算与物质模拟团队学科责任教授，中国人民大学

Professor, Department of Physics, Renmin University of China

主讲人简介/Biography:

卢仲毅，中国人民大学物理系教授，主要从事凝聚态物质的电子结构研究和计算方法发展，在铁基超导和量子多体理论等研究方面取得了一批有原创性的成果：提出了铁基超导的反铁磁超交换作用机理，正确预言了母体的反铁磁半金属特性，确认了FeTe和K2Fe3Se4的反铁磁长程序及电子结构；明确了铁磁金属层中量子阱态的共振隧穿等输运性质；提出了自然轨道重正化群方法，并应用于量子杂质系统的研究；用多体场论方法研究了几种自旋链系统的奇异特性。2007年获国家杰出青年基金资助，2012年聘为教育部长江学者特聘教授，2015年获教育部自然科学一等奖，同年获中国物理学会叶企孙物理奖，2019年获得国家自然科学奖二等奖。

Zhong-Yi Lu is a professor in the Department of Physics, Renmin University of China. His research interests include the electronic structure of condensed matter and the development of the related computational methods. He has made a number of original achievements in iron-based superconductivity and quantum many-body theory. He received his Ph.D. from the International School for Advanced Studies (SISSA) in Italy in 1996.  He was awarded the First Prize of Natural Science of the Ministry of Education in 2015, Ye Qisun Prize of Physics of Chinese Physical Society in the same year, and the second prize of National Natural Science Award in 2019. 

讲座摘要/Abstract:

在强关联电子材料中有许多新的量子现象。 如何理解和表征它们一直是凝聚态物理学的核心问题之一。 DFT+DMFT电子结构计算方法结合了基于密度泛函理论(DFT)的第一性原理电子结构计算和动力学平均场理论(DMFT)，被认为是研究强关联电子材料最有力和最有前途的方法。 但DFT+DMFT计算方法中的量子蒙特卡罗杂质求解器存在符号问题，这严重阻碍了DFT+DMFT的发展和应用。 另一方面，量子重正化群(RG)是研究多电子相互作用关联系统的最重要的和准确的方法之一。针对此，我们在自然轨道表示的框架内提出了一个新的概念以使重正化方法推广到一般轨道表示的抽象空间, 即自然轨道重正化群(NORG)。 我们表明，在求解一个量子杂质模型的低能态时，NORG的计算复杂度对电子库自由度是多项式的而不再是指数的。 此外，该方法还适用于具有任意晶格拓扑结构的量子杂质模型。 实际上，NORG的有效性基本上与模型的拓扑结构无关。 因此，NORG自然适合用于研究量子团簇-杂质模型。 这使得NORG成为动力学平均场理论DMFT的一个天然杂质求解器，从而帮助克服DFT+DMFT中的负符号问题。  

There are many novel quantum phenomena in strongly correlated electronic materials. How to understand and characterize them has always been one of the central topics in condensed matter physics. The DFT+DMFT electronic structure calculation method is considered to be the most powerful and promising method for studying strongly correlated electronic materials, which combines the first-principles electronic structure calculation based on the density functional theory (DFT) and the dynamical mean field theory (DMFT). Nevertheless, the DFT+DMFT calculation method now suffers the sign problem with its quantum Monte Carlo impurity solver, which seriously hinders the development and application of DFT+DMFT. On the other hand, the quantum renormalization group (RG) procedure is one of the most important and accurate approaches for studying interacting many-electron correlated systems, upon which we propose a new concept in the framework of natural orbitals so that we can generalize the RG into general orbital space, namely natural orbitals renormalization group (NORG). We show that the NORG takes a polynomial rather than exponential computational cost in the number of electron bath sites to solve the low-energy states of a quantum impurity model. Moreover, the NORG can work on a quantum impurity model with any lattice topological structure. Actually, the effectiveness of the NORG is basically irrespective of a model's topological structure. Thus, the NORG is naturally appropriate for studying quantum cluster-impurity model. This makes the NORG be a natural impurity solver to dynamical mean field theory.

讲座联系人/Contact:

理学院 张老师 zhangyue62@westlake.edu.cn