Anomalous behavior and structure of a liquid of particles interacting through the harmonic-repulsive pair potential near the crystallization transition

Abstract

A characteristic property of many soft matter systems is an ultrasoft effective interaction between their structural units. This softness often leads to complex behavior. In particular, ultrasoft systems under pressure demonstrate polymorphism of complex crystal and quasicrystal structures. Therefore, it is of interest to investigate how different can be the structure of the fluid state in such systems at different pressures. Here we address this issue for the model liquid composed of particles interacting through the harmonic-repulsive pair potential. This system can form different crystal structures as the liquid is cooled. We find that, at certain pressures, the liquid exhibits unusual properties, such as the negative thermal expansion coefficient. Besides, the volume and the potential energy of the system can increase during crystallization. At certain pressures, the system demonstrates high stability against crystallization and it is hardly possible to crystallize it on the timescales of the simulations. To address the liquid's structure at high pressures, we consider the scaled pair distribution function (PDF) and the bond-orientational order (BOO) parameters. The marked change happening with the PDF, as pressure increases, is the splitting of the first peak which is caused by the appearance of non-negligible interaction with the second neighbors and the following rearrangement of the structure. Our findings suggest that non-trivial effects, usually explained by different interactions at different spatial scales, can be observed also in one-component systems with simple one-length-scale ultrasoft repulsive interactions.Moscow Region, Russia nanoparticle systems raised interest in their simulations 4-25 . Model interactions in such systems, of course, can be quite different from typical interatomic interactions. One characteristic property of many soft matter systems is a finite repulsion even at vanishingly small separation distances between their structural units, i.e., many soft matter systems are ultrasoft. 7,8,10,11 .However, some properties of the systems composed of large molecules closely resemble certain phenomenons observed in the atomic systems. This is related, in particular, to the phenomenons of the glass transition and jamming. The similarities in the behaviors of these different systems open a possibility to test if the ideas developed for one type of systems are general enough to be valid for the systems of another type 4,5,20,23 . One model system allowing to address these issues is the system of particles interacting through the harmonic-repulsive pair potential. This and the other closely related potentials describe qualitatively ultrasoft effective repulsion between globular micelles, microgels, starlike polymer solutions and other similar structural units of soft matter systems 7,9,[15][16][17]19,20,20,21,21,23,24,26,27 .In our previous publication, we studied crystalline structures that form in the one-component system with the interaction between the particles described by the harmoni...

Anomalous behavior of two-dimensional Hertzian sphere system

“…At the same time, the diffusion anomaly at low density was more pronounced. Later, qualitatively similar results were obtained for a Hertzian sphere system with α = 2.0 as well [18,19].…”

Structure of the simple harmonic-repulsive system in liquid and glassy states studied by the triple correlation function

“…As it has been discussed already in Ref. [38], in the interval of temperatures T ∈ [0.0035 : 0.0050 the system exhibits an anomalous behavior, i.e., negative thermal expansion coefficient. The behavior of the curve exhibits a clear change in the region of temperatures T ∈ [0.0020 : 0.0025], i.e., in the interval closely corresponding to the glass transition temperature.…”

“…In this paper, we discuss the results only at one particular pressure, i.e., at P=1.8. At this pressure, the studied system exhibits remarkable stability against crystallization, i.e., we did not observe crystallization of the this system even in very long cooling runs [38].…”

“…In our previous publication, we, in particular, investigated the structure of the harmonic-repulsive liquid at selected densities using the BOOPS [38]. From the obtained results, in our view, it is difficult to understand intuitively the strengths of the orientational correlations and their dependence on the temperature.…”

“…One structural feature of many systems interacting through soft potentials is the splitting of the first peak in the PDF [18,38]. While this splitting is quite common in the soft-matter systems, it is unusual for one-component systems with strong repulsion at short distances.…”