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SUMMARY:Simulate to discover: from new chemistry under high pressure to no
 vel two-dimensional materials - Professor Maosheng Miao\, Department of Ch
 emistry and Biochemistry California State University Northridge\, Californ
 ia 91330\, USA
DTSTART:20180320T140000Z
DTEND:20180320T150000Z
UID:TALK101599@talks.cam.ac.uk
CONTACT:Georg Schusteritsch
DESCRIPTION:The periodicity of the elements and the non-reactivity of the 
 inner-shell electrons are two related principles of chemistry\, rooted in 
 the atomic shell structure. Within compounds\, Group I elements\, for exam
 ple\, invariably assume the +1 oxidation state\, and their chemical proper
 ties differ completely from those of the p-block elements. These general r
 ules govern our understanding of chemical structures and reactions. Using 
 first principles calculations\, we demonstrate that under high pressure\, 
 the above doctrines can be broken. We show that both the inner shell elect
 rons and the outer shell empty orbitals of Cs and other elements can invol
 ve in chemical reactions. Furthermore\, we show that the quantized orbital
 s of the enclosed interstitial space may play the same role as atomic orbi
 tals\, an unprecedented view that led us to a unified theory for the recen
 tly observed high-pressure electride phenomenon. In the last example for h
 igh-pressure chemistry\, we demonstrate that He can form stable compounds 
 with ionic crystals. The driving force for these reactions is not the loca
 l chemical bonds but rather the alternation of the long-range Coulomb inte
 ractions among ions while incorporating He atoms in the lattice. \n\nFurth
 ermore\, we show the development of an efficient method that can automatic
 ally explore the surface structures by virtue of structure swarm intellige
 nce. While applying the method on the "simple" diamond (100) surface\, we 
 discovered a hitherto unexpected surface reconstruction featuring self-ass
 embly of carbon nanotubes (CNTs) arrays. The intriguing covalent bonding b
 etween the neighboring tubes creates a unique feature of carrier kinetics 
 ---one dimensionality of hole states whereas two dimensionality of electro
 n states\, which may lead to novel design of superior electronics. Using v
 ery different approach\, we propose and demonstrate a large family of two-
 dimensional semiconductors (2DSC)\, all adopting the same structure and co
 nsisting of only main group elements. We demonstrate the attainability of 
 these materials\, and show that they cover a large range of lattice consta
 nts\, band gaps and band edge states\, therefore are good candidate materi
 als for heterojunctions. The new 2DSCs may pave a way toward fabrication o
 f 2DSC devices at the same thriving level as 3D semiconductors.\n
LOCATION:Goldsmiths 1\, Lecture Theatre\, Department of Materials Science 
 &amp\; Metallurgy
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