Contact dynamics

Macroscopic behaviors of granular materials strongly depend on inter-particle forces between granular particles, where an atomic-scale study [2,3] is needed to understand the inter-particle forces and the origin of inelastic collisions.

Approach: To study the microscopic mechanism of inelastic collisions, we simulate binary collisions between hydrogen-passivated silicon nanoclusters by MD simulations (Fig. 4), where we have found that the restitution coefficient becomes negative if their incident angles exceed a critical value [4]. We have explained this surprising result by using a viscoelastic model of nanoclusters, where the negative restitution coefficient is caused by a finite duration of contact. Therefore, our conclusion implies the breakdown of kinetic theory (where the contact duration is assumed to be zero and the restitution coefficient is given by a positive constant) and opens the door to a general framework of the kinetic theory.

Method overview: We used 3D MD simulations of hydrogen-passivated silicon nanoclusters, where a bond-order (3-body) potential, i.e. the Telsoff potential, is adopted to model both the hydrogen and silicon atoms. The applicant implemented the potential model to the numerical codes, drew the 3D-graphics by using the OpenGL libraries, and proposed the viscoelastic model of nanoclusters.