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Tuesday, August 12 • 11:00 - 13:00
Computational Methods I

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11:00-11:30

Invited: Atsushi Oshiyama
Large-Scale Real-Space Density-Functional Calculations: Moire-Induced Electron Localization in Graphene & Floating Electron States in SiC

Current architecture of supercomputers consists of a huge number of massively paralleled compute nodes. This situation demands us to make close and exciting collaboration among the fields of physical science, applied mathematics and computer science. Such collaboration we name COMPUTICS has been already started (http://computics-material.jp/index-e.html). I explain an example of such collaboration which allows us to perform electronic-structure calculations based on the density-functional theory (DFT) for tens-of-thousands atom systems. The scheme we have adopted is the real-space (RS) scheme in the density functional theory (DFT) combined with the pseudo-potential technique. Our code RSDFT highly optimized to the current architecture of the supercomputer was awarded ACM Gordon-Bell prize in peak performance in 2011.

After explaining the essence of RSDFT, I report on the two issues in semiconductor physics. First, our large-scale DFT calculations for twisted bilayer graphene (tBLG) reveal the existence of the critical twist angle above which the two graphene layers are essentially decoupled and below which the Dirac electrons are localized due to Moire pattern. Second, in SiC, our calculations clarify that the electron states of the conduction bands of covalent semiconductors are distributed mainly in the interstitial channels and that this floating nature leads to the experimentally observed band-gap variation and the anisotropic effective masses in various polytypes of SiC.

11:30-11:45
Open

11:45-12:00
Oral: Marco Bernardi
The First Picosecond after Sunlight Absorption in Si & GaAs from First-Principles Calculations
Co-authors: Derek Vigil-Fowler, Jeffrey B. Neaton, Steven G. Louie

12:00-12:15
Oral: Piotr Boguslawski
Gallium Vacancy & Mn & Fe Ions in GaN by GGA+U Calculations: How Big is +U Term?
Co-authors: Tomasz Zakrzewski, Oksana Volnianska

12:15-12:30
Oral: Wei Chen
Band Offsets of Lattice-Matched Semiconductor Heterojunctions through Hybrid Functionals & GW 
Co-authors: Karim Steiner, Alfredo Pasquarello 

12:30-12:45
Open

12:45-13:00
Open 

Session Chairs
JB

Jeffrey B. Neaton

Director of the Molecular Foundry & Senior Faculty Scientist, Lawrence Berkeley National Laboratory
Jeffrey B. Neaton received his Ph.D. in physics from Cornell University in 2000. After a postdoc at Rutgers University, and after having worked at Lawrence Berkeley National Laboratory as a postdoc and staff scientist at the Molecular Foundry, he joined the UC Berkeley faculty in 2014. He is currently Director of the Molecular Foundry, a Department of Energy Nanoscale Science Research Center at Lawrence Berkeley National Laboratory, where he is... Read More →

Speakers
AO

Atsushi Oshiyama

Professor, Department of Applied Physics, The University of Tokyo
Atsushi Oshiyama is a professor at Department of Applied Physics in The University of Tokyo. He has been working in the field of computational materials science and condensed matter physics (http://oshiyama.t.u-tokyo.ac.jp/index-e.html). He is interested in cross-disciplinary collaboration among materials scientists and computer scientists, and now heads a research project, Materials Design through Computics... Read More →


Tuesday August 12, 2014 11:00 - 13:00
Room 16A

Attendees (10)