Integral equation study of soft-repulsive dimeric fluids

TL;DR

This study uses integral equation theories to analyze the structure and anomalies of dimeric fluids with core-softened potentials, comparing predictions with Monte Carlo simulations to assess the theories' accuracy.

Contribution

It provides a comprehensive theoretical analysis of water-like anomalies in dimeric fluids using RISM and OZ theories, validated against simulation data.

Findings

Theories and simulations agree on the presence of anomalies at low elongations.

Integral equation theories accurately predict pressure and radial distribution functions.

Anomalies diminish with increasing dimer elongation, likely due to crystallization.

Abstract

We study fluid structure and water-like anomalies of a system constituted by dimeric particles interacting via a purely repulsive core-softened potential by means of integral equation theories. In our model, dimers interact through a repulsive pair potential of inverse-power form with a softened repulsion strength. By employing the Ornstein-Zernike approach and the reference interaction site model (RISM) theory, we study the behavior of water-like anomalies upon progressively increasing the elongation {\lambda} of the dimers from the monomeric case ({\lambda} = 0) to the tangent configuration ({\lambda} = 1). For each value of the elongation we consider two different values of the interaction potential, corresponding to one and two length scales, with the aim to provide a comprehensive description of the possible fluid scenarios of this model. Our theoretical results are systematically compared with already existing or newly generated Monte Carlo data: we find that theories and simulations agree in providing the picture of a fluid exhibiting density and structural anomalies for low values of {\lambda} and for both the two values of the interaction potential. Integral equation theories give accurate predictions for pressure and radial distribution functions, whereas the temperatures where anomalies occur are underestimated. Upon increasing the elongation, the RISM theory still predicts the existence of anomalies; the latter are no longer observed in simulations, since their development is likely precluded by the onset of crystallization. We discuss our results in terms of the reliability of integral equation theories in predicting the existence of water-like anomalies in core-softened fluids.