Woodruff School of Mechanical Engineering
COE/Structural Mechanics Seminar
Adaptive-Boost Molecular Dynamics Simulation Of Thermally Activated Motion of Crystal Imperfections
Prof. Shigenobu Ogata
Graduate School of Engineering Science, Osaka University, Osaka, Japan
Monday, March 3, 2014 at 2:00:00 PM
MRDC Building, Room 2404
Dr. Ting Zhu
We have developed an accelerated molecular dynamics (MD) method  to model atomic-scale rare events, such as thermally activated motion of solute atom, dislocation, and grain boundary in crystals. In this method, a smooth histogram of collective variables is first estimated by canonical ensemble molecular dynamics calculations, and then a temperature-dependent boost potential is iteratively constructed to accelerate the MD simulation. This method not only allows us to observe the rare events but also to evaluate the profile of free energy and trial frequency along the reaction coordinate. We employed this method to study carbon diffusion in bcc iron. The predicted temperature dependent diffusivities of carbon agree well with the experimental measurements. Even at low temperature for which no experimental data are available, the diffusivity can be evaluated accurately. Additionally, we study carbon diffusion inside the dislocation core in bcc iron, and demonstrate the applicability of the method to rare events on a rugged free-energy surface. We found that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction, but in a conjugate diffusion direction . We also demonstrate the applicability of this method to study the dislocation and grain boundary motions.  A. Ishii, S. Ogata, H. Kimizuka, J. Li, Phys. Rev. B 85, 064303 (2012).  A. Ishii, J. Li, S. Ogata, PLoS ONE 8, e60586 (2013).
Shigenobu Ogata is a Professor in the Department of Mechanical Science and Bioengineering at Osaka University, Japan. He is also a Professor at the Center for Elements Strategy Initiative for Structural Materials, Kyoto University. He received his PhD in Mechanical Engineering from Osaka University in 1998, and was a visiting scientist at the Massachusetts Institute of Technology in 2002. Prof. Ogata's research is focused on multiscale materials modeling through integration of the first principles, atomistic and continuum simulation methods. He received the Young Engineer Award from the Japan Society of Mechanical Engineers in 2004.
Refreshments will be served.