报告一题目：Natural Orbitals Renormalization Group and Dynamical Mean Field Theory

报 告 人：卢仲毅 教授

          国家杰出青年基金获得者

          中国人民大学物理系

Abstract: One of the most important and accurate approaches for studying interacting many-electron correlated systems is the quantum renormalization group (RG) procedure, 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 and it 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. By using the NORG, we have recently solved the two-impurity Kondo problem, a long-standing problem in which there is the competition between the two opposite tendencies in the formation of a singlet ground state, driven respectively by the single-ion Kondo effect with conduction electrons to screen impurity spins and the RKKY interaction between the two impurities to directly form impurity spin singlet. The NORG is a natural impurity solver to dynamical mean field theory, which I will also introduce in this talk.

报告人简介：卢仲毅于1996年在意大利国际高等研究院(SISSA)获得凝聚态物理学哲学博士学位。毕业后，先后在美国能源部Ames国家实验室、Vanderbilt大学物理系和Oak Ridge国家实验室计算机科学和数学部工作。2005年1月聘为中国科学院理论物理研究所研究员和博士生导师。2007年1月聘为中国人民大学教授、物理系材料计算与物质模拟团队学科责任教授和召集人。主要从事电子结构计算方法及其并行化算法以及分子动力学模拟方法的研究以及这些方法在实际系统中的应用。

报告二题目：The Quantum-disordered Phase of Dense Ice Characterized by Synchrotron Infrared Spectroscopy and Ab Initio Theory

报 告 人：刘振先 博士

The Geophysical Laboratory of the Carnegie Institution of Washington

Abstract: Hydrogen bonds play a fundamental role for understanding the evolution from distinct molecular phases VII and VIII to a non-molecular centro-symmetric dense ice phase X under high pressure. However, insights of detailed transition mechanism to stable phase X remains unsettled. Here we present new evidence based on high-pressure infrared spectroscopy and first-principles theory calculations that a distinct proton quantum-disordered intermediate phase dominated by proton zero-point energy is identified from 60 to 80 GPa at room temperature. Significant changes of the bending and stretching vibrational bands are observed around 40 GPa at the onset of the intermediate phase. These two bands disappeared at 60 GPa indicating the dissociation of H2O molecules. Above 80 GPa, far-infrared reflectivity and absorptivity spectra reveal clear onset of phase X. However, the mixed X and quantum disordered phases persist up to the highest pressure studied. Ab initio theoretical characterization of the potential barrier for the proton in the hydrogen bond and the calculation of vibrational dynamics of structurally closely related ice VIII employing a first-principles linear response method provides a detailed interpretation of the infrared spectra of ice over the experimental pressure range from 3 to 102 GPa.

报告人简介：Zhenxian Liu is a lead beamline scientist for the Frontier Synchrotron Infrared Spectroscopy Beamline under Extreme Conditions (FIS), currently under construction at National Synchrotron Light Source II, Brookhaven National Laboratory. FIS is the successor of U2A beamline, a dedicated high-pressure infrared diamond anvil cell facility at NSLS, which has been managed by Geophysical Laboratory since 1999. He develops novel experimental techniques (e.g., vacuum far-IR spectroscopy down to 30 cm-1 at high pressure) and assists users in carrying out research projects in geoscience, planetary science, materials science, condensed matter physics, chemistry, and biology. He also uses synchrotron infrared spectroscopy, Raman scattering, photoluminescence as well as synchrotron x-ray diffraction techniques to explore physical and chemical properties and phase transitions of hydrous minerals, simple molecular systems, and nanoscale materials at high pressures and variable temperatures.

地 点：前卫南区唐敖庆楼C区603报告厅

时 间：2016年3月25日（周五）下午2:00

举办单位：超硬材料国家重点实验室

          物理学院

          原子与分子物理研究所

          吉林省物理学会

          中国物理学会高压物理专业委员会