Understanding fragility in supercooled Lennard-Jones mixtures. I. Locally preferred structures

Abstract

We reveal the existence of systematic variations of isobaric fragility in different supercooled Lennard-Jones binary mixtures by performing molecular dynamics simulations. The connection between fragility and local structures in the bulk is analyzed by means of a Voronoi construction. We find that clusters of particles belonging to locally preferred structures form slow, long-lived domains, whose spatial extension increases by decreasing temperature. As a general rule, a more rapid growth, upon supercooling, of such domains is associated to a more pronounced super-Arrhenius behavior, hence to a larger fragility.

Observation of crystallization slowdown in supercooled parahydrogen and orthodeuterium quantum liquid mixtures

“…A number of simulation studies [15,17,18,28] have suggested that in one possible scenario crystallization might be hindered by the emergence in the bulk supercooled liquid of locally preferred structures that eventually are incompatible with long-range crystalline order [34]. One important example is the icosahedron with its fivefold symmetry [35], which has been recently found to be a fundamental geometrical motif in the structure of bulk metallic glasses [36].…”

“…As the next step we looked at the bulk structural features, which offer important insights into the behavior of supercooled liquids [4,15,17,28]. To access static structural properties of the nonequilibrium pH 2 -oD 2 quantum liquid mixtures we have carried out path-integral Monte Carlo (PIMC) simulations [29] by using a canonical [30] Worm algorithm [31].…”

“…Indeed, classical binary systems of particles that interact via a simple LennardJones (LJ) pair potential have been widely employed as the simplest theoretical models to investigate crystallization and glassy behavior in supercooled liquids [15][16][17][18][19]. Due to the spherical symmetry of the ground-state wave function of the pH 2 and oD 2 molecules, which are characterized by an even rotational quantum number J [20], a pH 2 -oD 2 mixture provides a neat molecular binary system in which the pair interactions can be described by the same isotropic LJ potential [20].…”

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

“…(17), when i = 8, q 8,R ≈ 2.137σ 1 > 2σ 1 , (q 7,R < 2σ 1 ), and q 8,R -q 1 ≈ 2.032 σ 1 > 2σ 1 . Therefore, only in the 8th order of L-J potential field, the spacing between the 8th order and the first order of sharp-angled point is more than 2σ 1 and is able to place a σ 1 hard-cluster in between.…”

“…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.…”