Two Bond-Exchange modes in sodium silicate liquids.

• This study introduces the function that can quantitatively analyze bond-exchange. • I found two distinct bond exchange modes in silicate liquids. • One mode contributes diffusion, whereas the other mode does not. Because of their network structure, the diffusion mechanism of network-forming elements, namely silicon and oxygen, remains unclear. Several diffusion mechanisms have been proposed based on molecular dynamics simulations; however, the bond-exchange motion has not been quantitatively analyzed. This study introduces the concept of bond-breaking/forming particles. By treating the bond-breaking/forming events as instant particles, the bond-exchange event can be interpreted as a pair-correlation function of these particles. Here, examples of sodium silicate liquids at various pressures are presented using the results of force-field molecular dynamics simulations. Analyses of the pair correlation of bond-breaking/forming particles revealed two distinct bond-exchange modes. Only the short mode contributed to the diffusion of the network-forming elements based on comparative analysis of the pressure dependence of the integrated peaks of the pair-correlation functions and the self-diffusion coefficients of silicon. [ABSTRACT FROM AUTHOR]