The variation with respect to temperature T of transport properties of 58 fragile structural glass-forming liquids (67 data sets in total) are analyzed and shown to exhibit a remarkable degree of universality. In particular, super-Arrhenius behaviors of all supercooled liquids appear to collapse to one parabola for which there is no singular behavior at any finite temperature. This behavior is bounded by an onset temperature T(o) above which liquid transport has a much weaker temperature dependence. A similar collapse is also demonstrated over the smaller available range for existing numerical simulation data.

We report quantum five-dimensional (5D) calculations of the energy levels and wave functions of the hydrogen molecule, para-H2 and ortho-H2, confined inside the small dodecahedral (H2O)20 cage of the sII clathrate hydrate. All three translational and the two rotational degrees of freedom of H2 are included explicitly, as fully coupled, while the cage is treated as rigid. The 5D potential energy surface (PES) of the H2-cage system is pairwise additive, based on the high-quality ab initio 5D (rigid monomer) PES for the H2-H2O complex. The bound state calculations involve no dynamical approximations and provide an accurate picture of the quantum 5D translation-rotation dynamics of H2 inside the cage. The energy levels are assigned with translational (Cartesian) and rotational quantum numbers, based on calculated root-mean-square displacements and probability density plots. The translational modes exhibit negative anharmonicity. It is found that j is a good rotational quantum number, while the threefold degeneracy of the j = 1 level is lifted completely. There is considerable translation-rotation coupling, particularly for excited translational states.

We generalize the simplest kinetically constrained model of a glassforming liquid by softening kinetic constraints, allowing them to be violated with a small rate. We demonstrate that this model supports a first-order dynamical (space-time) phase transition between active (fluid) and inactive (glass) phases. The first-order phase boundary in this softened model ends in a finite-temperature dynamical critical point, which may be present in natural systems. In this case, the glass phase has a very large but finite relaxation time. We discuss links between the dynamical critical point and quantum phase transitions, showing that dynamical phase transitions in d dimensions map to quantum transitions in the same dimension, and hence to classical thermodynamic phase transitions in d þ 1 dimensions. critical behavior | supercooled liquidsA s a liquid is cooled through its glass transition, it freezes into an amorphous solid state, known as a glass (1, 2). The transition from fluid to solid typically requires only a small change in temperature and is accompanied by characteristic large fluctuations, known as dynamical heterogeneity (3). Based on these observations, several theories invoke analogies between the glass transition and phase transitions that occur in model systems (4-8). Some theories are based on equilibrium phase transitions at finite temperatures (4, 5, 7), although these seem to be unobservable in experiments and computer simulations. An alternative idea (8) is that supercooled liquids and certain model systems both exhibit dynamical phase transitions (9-14), controlled by biasing fields that drive the system away from equilibrium. Here, we demonstrate the existence of a nontrivial critical point associated with such a dynamical transition.The phase transition that we consider occurs in trajectory space. We bias the system toward an "ideal glass" phase by enhancing the probability of trajectories where particle motion is slow. The parameter that controls this bias-the field s-can be varied continuously in computer simulations. For models of glass-forming liquids, the response to this change can be large and discontinuous, corresponding to a first-order phase transition. Such transitions between an active state (analogous to a fluid) and an inactive state (analogous to a glass) were first demonstrated (11) for kinetically constrained lattice models (KCMs) (15). More recently, evidence for such a transition has been found in the molecular dynamics of an atomistic model of a supercooled liquid (13).In KCMs, the transition to the inactive phase takes place when the biasing field s is infinitesimally small, and this result is independent of the temperature. However, very general arguments based on ergodicity breaking, e.g., refs. 14, 16 and 17, indicate that transitions in ergodic molecular fluids should take place at nonzero s. In this context, the essential difference between KCMs and molecular systems is that forces constraining dynamics in the former are infinite (i.e., hard) whereas those in the latter ar...

The earlier paper of this same title demonstrated a collapse of relaxation data of fragile supercooled glass forming liquids [J. Phys. Chem. B 2009, 113, 5563-5567]. For temperature T below that of the onset to supercooled behavior, T(o), the logarithm of structural relaxation time, log τ, is given by the parabolic form log(τ/τ(o)) = J(2)(1/T - 1/T(o))(2), where J and τ(o) are temperature-independent. This paper presents further applications of this formula. In particular, it is shown that the effects of attractive forces in numerical simulation of glass-forming liquids can be logically organized in terms of J and T(o). Further, analysis of experimental data for several systems suggests that J and T(o) are material properties. In contrast, values of similar parameters for other fitting formulas are shown to depend not only upon the material but also upon the range of data used in fitting these formulas. Expressions demonstrated to fail in this way include the Vogel-Fulcher-Tammann formula, a double-exponential formula, and a fractional exponential formula.