The persistence of bonds for long times in a tetravalent saturated square-well model network fluid is studied from the gas to the glass transition by molecular dynamics simulation. The time correlation function for bonds fits a stretched exponential decay in time c(f) = exp (- (t/tp)β), which yields a persistence time tp. The time for c(t) to decay to zero, about 10tp, is a measure of the equilibration time, and corresponds to the time required for the root-mean-square displacement of the molecules to reach four molecular diameters. At liquid-like densities and for the temperature range covered, tp scales approximately as the inverse self-diffusion coefficient over four orders of magnitude. When the well depth ε/kT is large, tp has an Arrhenius temperature dependence along isobars, a characteristic of strong liquids like SiO2, but when ε/kT = 0, the isobaric temperature dependence has the non-Arrhenius form of a more fragile liquid, like o-terphenyl.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Condensed Matter Physics
- Physical and Theoretical Chemistry