Collective dynamics of simple liquids: A mode-coupling description

Abstract

We use the mode-coupling theory (MCT), which has been highly successful in accounting for the anomalous relaxation behaviour near the liquid-to-glass transition, for describing the dynamics of monatomic (i.e. simple) liquids away from the glass formation regime. We find that the dynamical structure factor predicted by MCT compares well to experimental findings and results of computer simulations. The memory function exhibits a two-step decay as found frequently in experimental and simulation data. The long-time relaxation regime, in which the relaxation rate strongly depends on the density and is identified as the α relaxation. At high density this process leads the glass instability. The short-time relaxation rate is fairly independent of density.

Liquid boron: X-ray measurements andab initiomolecular dynamics simulations

“…The agreement is good at low Q but, at Q's around the peak of S͑Q͒, the AIMD predicts a higher value, indicating a narrower shape to S͑Q , ͒. The value extrapolated to low Q, l = 15 mPa s, is appreciably higher than in alkali metals but only slightly higher than other group-13 metals, Al and Ga. 35 We now address the applicability of the densityfluctuation version of MCT, previously employed successfully to describe the glass transition in liquids 39,40 and more recently to the dynamics of liquids in equilibrium, 5,6 to liquid boron. The generalized longitudinal viscosity obtained from the application of the MCT to the memory function in Eq.…”

“…5,6 In both cases the details of the interatomic potential are important: the occurrence of a liquid-liquid transition appears to require a potential with either two distinct shortrange repulsive distances 7 or a repulsive soft core 8 while the MCT seems to work best if the potential can be approximated by a smoothed hard-sphere interaction. 6 Relatively little is known about liquid boron due in part to its high melting point.…”

“…5,6 In both cases the details of the interatomic potential are important: the occurrence of a liquid-liquid transition appears to require a potential with either two distinct shortrange repulsive distances 7 or a repulsive soft core 8 while the MCT seems to work best if the potential can be approximated by a smoothed hard-sphere interaction. 6 Relatively little is known about liquid boron due in part to its high melting point. The existence in the solid of ␣-rhombohedral and ␤-rhombohedral crystal structures, which can be regarded as high-density and low-density phases, 9,10 suggests the possibility of high-density and lowdensity phases in the liquid.…”

Rattling the cage: Micro- to mesoscopic structure in liquids as simple as argon and as complicated as water

“…In the supercooled region, the lineshape of the α relaxation is typically stretched (i.e., broadened with respect to a Debye function) but the lineshape and amplitude are temperature-independent above T C . [65][66][67][68] Extending MCT to include the terahertz region is still challenging, and inevitably results in less meaningful fitting models, and we therefore use more conventional but readily interpreted phenomenological models. Even so, the contributions to the low-frequency spectrum are very difficult to disentangle and one of our aims is to identify the individual contributions through simplifying the spectra.…”

Soft matrix and fixed point of Lennard-Jones potentials for different hard-clusters in size at glass transition

“…Lennard -Jones (L-J) potential is widely used to describe molecule-cluster interactions and glass transition (GT), [1][2][3][4][5][6] However, the fundamental theory to unify the mechanisms for the truncated L-J potential, 7-9 the presence of long-ranged interparticle potentials, 10 the density or cluster size fluctuation stability, 11 and the two kinds of relaxations: fast and slow in current Mode-Coupling Theory, 12 the distribution of particle sizes, 13 or the core difficulty of particle size fractionation 14 in simulation are still not simply and fully established. The relationship between GT and general displacement transitions in condensed matter physics has remained obscure.…”