John Kieffer

Professor

kieffer@umich.edu

2018 HH Dow

T: (734) 763-2595

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Atomistic Simulations of Nucleation and Crystal Growth Phenomena

Sponsor: National Science Foundation
This project is to use computer simulations to study structural transitions under conditions that are inaccessible to experiments, such as materials subject to very high pressure and/or high temperature, and to address some long-standing problems in materials science. <br>Classical molecular dynamics (MD) simulation is the major tool used in this project. In order to do large-scale computer simulations, parallel MD codes (FLX) have been developed by using spatial decomposition scheme in MPI. A new type of reactive interaction potential has been designed for this project. There are three main features of this potential: (1) three-body interaction, the directional character of the covalent bonding is modeled by means of three-body terms; (2) dynamic charge redistribution, a charge transfer term controls the degree of charge polarization in a covalent bond, as well as the amount of charge transferred between atoms upon rupture or formation of such a bond; (3) effective coordination number, both two- and three-body interactions depend on the local environment of an atom, which is described by the number of nearest neighbors of an atom. This potential is especially suitable for simulating systems with multiple coordination states, like SiO2 and B2O3.<br>Through this project, we have gained detailed insights and provided mechanistic explanations concerning the following issues in materials science:<br>&nbsp;&nbsp;&nbsp;(1)thermally induced structural transformations in crystalline silica and the origin of the negative thermal expansion in high-temperature polymorphs of silica;<br>&nbsp;&nbsp;&nbsp;(2)pressure-induced crystalline to crystalline/amorphous transformations in silica, densification mechanisms and the nature of high-pressure phases;<br>&nbsp;&nbsp;&nbsp;(3)dynamic properties of molten silica;<br>&nbsp;&nbsp;&nbsp;(4)structural origin of the anomalous thermo-mechanical properties of silica glass (e.g. increase of the mechanical moduli upon expansion and negative thermal expansion under pressure);<br>&nbsp;&nbsp;&nbsp;(5)nature of polyamorphic transitions in network glasses such as SiO2 and B2O3.