2 research outputs found
Molecular Dynamics Simulations of a Pressure-induced Glass Transition
We simulate the compression of a two-component Lennard-Jones liquid at a
variety of constant temperatures using a molecular dynamics algorithm in an
isobaric-isothermal ensemble. The viscosity of the liquid increases with
pressure, undergoing a broadened transition into a structurally arrested,
amorphous state. This transition, like the more familiar one induced by
cooling, is correlated with a significant increase in icosahedral ordering. In
fact, the structure of the final state, as measured by an analysis of the
bonding, is essentially the same in the glassy, frozen state whether produced
by squeezing or by cooling under pressure. We have computed an effective
hard-sphere packing fraction at the transition, defining the transition
pressure or temperature by a cutoff in the diffusion constant, analogous to the
traditional laboratory definition of the glass transition by an arbitrary, low
cutoff in viscosity. The packing fraction at this transition point is not
constant, but is consistently higher for runs compressed at higher temperature.
We show that this is because the transition point defined by a constant cutoff
in the diffusion constant is not the same as the point of structural arrest, at
which further changes in pressure induce no further structural changes, but
that the two alternate descriptions may be reconciled by using a thermally
activated cutoff for the diffusion constant. This enables estimation of the
characteristic activation energy for diffusion at the point of structural
arrest.Comment: Latex using Revtex macro