报告题目：The change of basic chemical behavior of elements under high pressure

报告人：Maosheng Miao, Assistant Professor

Departmentof Chemistry and Biochemistry, California State University Northridge

BeijingComputational Science Research Center, Beijing, China

报告时间：2019年7月9日（星期二）上午9:30

报告地点：前卫南区物理楼333报告厅

主办单位：物理学院

报告摘要：

The chemistry at ambient condition has implicit boundaries rooted in theatomic shell structure: the inner-shell electrons and the unoccupiedouter-shell orbitals do not involve as major component in chemical reactionsand in chemical bonds. The chemical properties of atoms are determined by the electronsin the outermost shell; hence, these electrons are called valence electrons.These general rules govern our understanding of chemical structures andreactions.

Using first principles calculations, we demonstrate that under highpressure, the above doctrines can be broken. We show that both the inner shellelectrons and the outer shell empty orbitals of Cs and other elements caninvolve in chemical reactions. In the presence of fluorine and under pressure,the formation of CsFn (n > 1) compounds containing neutral or ionicmolecules is predicted. Their geometry and bonding resemble that ofisoelectronic XeFn molecules, showing a cesium atom that behaves chemically likea p-block element under these conditions. Furthermore, we find that under high pressureHg in Hg-F compounds transfers charge from the d orbitals to the F, thus behavingas a transition metal. Oxidizing Hg to + 4 and + 3 yielded the thermodynamicallystable compounds HgF4 and HgF3. The former consists of HgF4 planar molecules.HgF3 is metallic and ferromagnetic, with a large gap between its partiallyoccupied and unoccupied bands under high pressure.

In other works, we find that Xe, Kr, and Ar can form thermodynamicallystable compounds with Mg at high. The resulting compounds are metallic and thenoble gas atoms are negatively charged, suggesting that chemical species with acompletely filled shell can gain electrons, filling their outermost shell(s).Similarly, we predicted that pressure can cause large electron transfer fromlight alkali metals such as Li to Cs, causing Cs to become anionic with aformal charge much beyond -1.

Furthermore, we show that the quantized orbitals of the enclosedinterstitial space may play the same role as atomic orbitals, an unprecedentedview that led us to a unified theory for the recently observed high-pressureelectrode phenomenon. In the last example for high-pressure chemistry, wedemonstrate that He can form stable compounds with ionic crystals. The drivingforce for these reactions is not the local chemical bonds but rather thealternation of the long-range Coulomb interactions among ions while incorporatingHe atoms in the lattice.

报告人简介：

Dr. Maosheng Miao obtained his Ph.D. in physical chemistry at JilinUniversity in China. He has more than 20 years working experience andbackground in first principles calculations of the atomic and electronicstructures of materials and solid-state chemistry. He has worked in many areasof computational materials science, ranging from semiconductor defects,surfaces and interfaces, functional oxides, solid-state lighting materials,two-dimensional materials, high pressure physics and chemistry, to methoddevelopments, including structure search methods and local pseudopotentials. Hehas published more than 100 papers in top journals and has an H-index of 32.His discovery of new chemical bonds formed by Cs 5p electrons was reported byScientific American and highlighted by Nature Chemistry and Nature China. Hiswork provided a unified mechanism for the striking phenomenon of high-pressure electridesand was highlighted by JACS and Nature Chemistry. His work on Hg-F compounds inwhich Hg behaves as a transition metal was assessed as top 5% by AngewandteChemie and was selected as a back cover. His work proposing a method to improvethe performance of high electron mobility transistors (HEMT) was reported byCompound Semiconductor.