Group connectivity in binary silicate glasses: A quasi-chemical approach and molecular dynamics simulation

Abstract The medium-range order of molecular dynamics (MD) simulated binary alkali silicate glass with 5, 10, 15, 20, 25, and 33.3 mol% of Na 2 O is studied in terms of the connectivity groups Q n , a 1 , … , a n , where n stands for the number of bridging oxygen atoms, and a 1 , …, a n indicate the type of the connected Q n units. MD structure significantly deviates from the random connectivity model. The deviations were quantified by means of the quasi-chemical approach. The interchange energy between Q 3 and Q 4 units was found to be negative, indicating preferential formation of Q 3 –Q 4 connections. This means that no tendency to phase separation was observed. Although alkali cations were apparently non-homogeneously distributed in space, regions abounding in Q 3 –Q 3 and Q 4 –Q 4 connections were not formed. It was suggested that grouping of alkali cations can be also mediated by the Q 4, 4433 groups.