We have studied the diffusion mechanism in network-forming liquids via molecular dynamics simulation. Two models of silica liquid at temperatures of 2600 and 3500 K have been constructed. | VNU Journal of Science: Mathematics – Physics, Vol. 32, No. 4 (2016) 32-39 Simulation of Diffusion Mechanism and Heterogeneous Dynamics in Network-forming Liquid Nguyen Thi Thanh Ha1,*, Nguyen Anh Dung2, Nguyen Quang Bau3, Pham Khac Hung1 1 Department of Computational Physics, Hanoi University of Science and Technology, Vietnam 2 Facutly of Electrical Engineering Technolog, Hanoi University of Industry 3 Department of Physics, Hanoi National University, Hanoi, Vietnam Received 18 November 2016 Revised 16 December 2016; Accepted 28 December 2016 Abtract: We have studied the diffusion mechanism in network-forming liquids via molecular dynamics simulation. Two models of silica liquid at temperatures of 2600 and 3500 K have been constructed. The motion of atoms is analyzed through reactions SiOx SiOx 1, OSiy OSiy 1 and coordination cells. It was shown that the reactions happen not randomly in the space, but they occur more frequently with some coordination cells and bonds Si-O. This effect enhances upon lowering the temperature. The number of reactions happening in the coordination cells is strongly correlated with the mobility of CC atom. We found that there are large rigid clusters which compose of immobile atoms and exist for long time. Further, the dynamics heterogeneity (DH) is determined via sets of: (1) most mobile or immobile atoms; (2) atoms belonging to large rigid clusters. We show that the percolation rigid cluster responds to the dynamical slowing down present near glass-transition. Keywords: Simulation, silica, liquid, dynamic heterogeneity, rigid cluster. 1. Introduction The glass-forming liquids, when cooled down below melting point fast enough, will form a glass at the temperature Tg called the glass-transition temperature. Close to the glass-transition, the structure of these liquids appear to change subtly but dynamical properties . the structural relaxation time, the diffusion constant, and the viscosity increase by orders of magnitudes .
