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arXiv 1612.05089cond-mat.softcond-mat.stat-mech
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软排斥二聚体流体的积分方程研究

Integral equation study of soft-repulsive dimeric fluids

Gianmarco Munaò, Franz Saija

摘要:

利用积分方程理论研究了二聚体粒子通过纯排斥核软化势相互作用系统的流体结构和类水反常现象。在我们的模型中,二聚体相互作用通过一个排斥对势的反幂形式与软化的排斥强度。采用Ornstein-Zernike方法和参考相互作用位点模型(RISM)理论,研究了二聚体从单体构型(λ = 0)到正切构型(λ = 1)伸长λ逐渐增大时的类水反常行为.对于每个值的伸长率,我们考虑两个不同的值的相互作用的潜力,对应于一个和两个长度尺度,目的是提供一个全面的描述可能的流体的情况下,该模型。我们的理论结果与已有的或新生成的Monte Carlo数据进行了系统的比较:我们发现,理论和模拟一致提供了一个流体的图像,表现出密度和结构异常的低λ值和两个值的相互作用势。积分方程理论给出了准确的预测压力和径向分布函数,而温度发生异常被低估。在增加伸长率时,RISM理论仍然预测存在异常;后者在模拟中不再观察到,因为它们的发展可能被结晶的开始所阻止。我们讨论了我们的结果的可靠性积分方程理论在预测存在的水样异常的核心软化流体。

英文摘要:

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 λ of the dimers from the monomeric case (λ = 0) to the tangent configuration (λ = 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 λ 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.

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