To clarify the local environment of atoms, we apply the oxygen simplex (OS) which is characterized by the size, forming oxygen atom types and the number of sodium atoms located inside the OS. The simulation shows that the liquid comprises the Si-O network and sodium atoms are distributed through different OS types forming by four O atoms. | VNU Journal of Science Mathematics Physics Vol. 36 No. 2 2020 47-54 Original Article Structural and Dynamics Heterogeneity in Sodium Silicate Liquid Nguyen Thu Nhan Mai Thi Lan Hanoi University of Science and Technology 1 Dai Co Viet Hanoi Vietnam Received 14 November 2019 Revised 30 December 2019 Accepted 04 March 2020 Abstract Liquid Na2O-4SiO2 has been constructed by molecular dynamics simulation at 1873 K ambient pressure with periodic boundary conditions. To clarify the local environment of atoms we apply the oxygen simplex OS which is characterized by the size forming oxygen atom types and the number of sodium atoms located inside the OS. The simulation shows that the liquid comprises the Si-O network and sodium atoms are distributed through different OS types forming by four O atoms. The number of sodium in particular simplex depends on the size and types of OS. There are five types of OS corresponding to values of n 0 4. Here n is number of bridge oxygens which an OS passed through. We also found that the OSs are connected to each other form a long channel where hundreds of sodium atoms move. The observed distribution of sodium through Si-O network clearly indicates the structural and dynamics heterogeneity in sodium silicate liquid. Keywords Simulation oxygen simplex sodium silicate structural heterogeneity. 1. Introduction Network-forming liquid of SiO2 with an alkali oxide such as Na2O Li2O or K2O are of general interest for the study of ion transport mechanisms in silicates 1-21 . It is related to the ionic conductivity capable viscosity and diffusivity of material. The Si and O atoms form a disorder tetrahedral network and sodium atoms fill into this network and to be network modifier atoms 1 2 . The diffusion coefficient of Si and O atom is very small about 10-5 cm2 s and the one of Na is larger 3 4 . Thus Si and O atoms are immobility atoms and Na atoms are mobility atoms. The distribution of atoms Na in space is main cause of structural and .
