Equilibrium phase diagram of a randomly pinned glass-former

Misaki Ozawa, Walter Kob, Atsushi Ikeda, Kunimasa Miyazaki

We use computer simulations to study the thermodynamic properties of a glass-former in which a fraction c of the particles has been permanently frozen. By thermodynamic integration, we determine the Kauzmann, or ideal glass transition, temperature TK(c) at which the configurational entropy vanishes. This is done without resorting to any kind of extrapolation, i.e., TK(c) is indeed an equilibrium property of the system. We also measure the distribution function of the overlap, i.e., the order parameter that signals the glass state. We find that the transition line obtained from the overlap coincides with that obtained from the thermodynamic integration, thus showing that the two approaches give the same transition line. Finally, we determine the geometrical properties of the potential energy landscape, notably the T- and c dependence of the saddle index, and use these properties to obtain the dynamic transition temperature Td(c). The two temperatures TK(c) and Td(c) cross at a finite value of c and indicate the point at which the glass transition line ends. These findings are qualitatively consistent with the scenario proposed by the random first-order transition theory.