Speaker: Feng Zhang (Ames Laboratory)

Title: Atomistic modeling of crystal nucleation and its applications in materials and Earth sciences

Abstract: Homogeneous nucleation of a crystalline phase from moderately supercooled liquid is a typical rare event and is inaccessible within the timescales of conventional molecular dynamics (MD) simulations. In this talk, we present a “persistent embryo” method (PEM) to facilitate crystal nucleation in MD simulations. In PEM, a small crystal embryo is inserted into the liquid, with spring forces applied to keep the embryo from melting. The springs are graduated weakened as the embryo grows and are completed removed when the nucleus size remains significantly smaller than the critical size.  In this way, one can observe the spontaneous fluctuations of a critical nucleus in an unbiased environment, without any assumptions on the shape of the critical nucleus. We apply this method to metallic and soft-matter systems and obtain results that compare favorably with experiments and other simulation methods. In addition, we demonstrate a possible two-step nucleation mechanism of molten iron in Earth’s core, which could resolve the well-known “inner core nucleation paradox”.

Bio: I obtained a B.S. degree in 1999 and M.S. in 2002, from Nanjing University of China. After that, I came to the United States and earned my Ph.D. degree in Physics at the Pennsylvania State University in 2008. I worked as a postdoctoral fellow at Georgia Institute of Technology from 2008 to 2011, before joining the Materials Science and Engineering Division of Ames Lab, first as a postdoctoral research associate and then a staff scientist since 2016. 

I have worked on modeling materials behaviors with various computational tools, from first-principles calculations to larger-scale atomistic modeling using empirical potentials. More recently, I also have research interest in developing ab initio methods for strongly correlated systems and quantum computing.