Medium range order and configurational entropy of vitreous silica

摘要： Two potential sets and three thermodynamic regimes were utilized in molecular dynamics simulations in the preparation of the corresponding structures of vitreous silica. Medium range order characterized by means of basic ring distributions is robust to both thermodynamic conditions and/or potentials sets. A strong correlation between topology and geometry is demonstrated; the correlation is much stronger for simple clusters/small rings. Configurational entropy was evaluated by the ideal mixing of the structural units of the decomposed silica network. Entropy responds to alterations in the heating/cooling rates and its behaviour yields an excellent agreement with the experimental specific heat capacity drops observed at the glass transition. It is suggested the glass transition of the simulated glass should be identified with the change of entropy and not with a change of enthalpy as is conventionally done.