engleski

Water-like structure with repulsive double-core interactions

It is known that some spherical pair interactions are able to reproduce several of structural and physical properties of complex liquids. For example, soft-core repulsive interactions with an attractive well display the liquid-liquid coexistence with a critical point and water-like density anomaly [1]. Similarly, competing interactions (short-range attraction with long-range repulsion) reproduce self-organization with different morphologies such as stripes, network and cluster formations [2]. In this study, we show that a simple core-softened interaction, namely a soft-core 1/r12 interaction together with Gaussian repulsion, is able to reproduce the major features of radial distribution function and the structure factor of water, hence suggesting that such repulsive interaction is able to mimic the structure of real water [3]. We use both Monte Carlo simulations and the well known Percus-Yevick (PY) and Hypernetted-chain (HNC) integral equation theories. This study indicates that the structure of liquid water can be seen as the result of the two competing interactions, with two length scales: the diameter of the oxygen atom and the length of the hydrogen bond. It also indicates that this competition is not confined to near-neighbours, but is very (possibly infinitely) long ranged. It implies a very peculiar form of the density correlations and thus the cluster-structure of this particular liquid. This is indeed confirmed by the outcome of the integral equation studies. The HNC equation is able to reproduce the structure with puzzling accuracy -in view of its lesser accuracy when the Gaussian core is removed. In contrast, the PY equation has no solution for this state point ; it does at higher temperatures, but with dramatic inaccuracy, a result of its insufficient diagrammatic structure. These facts point to the intriguing nature of the density correlations in water, which remains -to date- largely unexplored. [1] Franzese G., “Differences between discontinuous and continuous soft-core attractive potentials: The appearance of density anomaly” , Journal of Molecular Liquids, 136, 267-273 (2007) [2]. Seul M and Andelman D., “Domain shapes and patterns: The phenomenology of the modulated phase”, Science, 267, 476-483 (1995) [3] Perera A., Rispe A., Zoranic L., Mazighi R. and Sokolic F., “Water-like structure with repulsive double-core interactions“, Molecular Physics, in press

soft-core potential; integral equations; water

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