A spherical model with directional interactions. I. Static properties.
A spherical model with directional interactions. I. Static properties.
复制标题
具有定向相互作用的球形模型。
DOI：
10.1063/1.2799522
复制
发表时间：
2007
期刊：
影响因子：
--
通讯作者：
P. Tartaglia
中科院分区：
文献类型：
--
作者：
E. Zaccarelli;F. Sciortino;P. Tartaglia
我们介绍了一个简单的球形模型，其结构特性与定向相互作用的模型所产生的相似，通过采用大小硬球的二元混合物，仅在不同大小的粒子之间作用方阱吸引力。小颗粒提供了大颗粒之间的结合。通过适当选择相互作用参数以及两种物质的相对浓度，可以控制有效价态。在这里，我们专注于一个特定的选择有利于四面体有序的参数，并研究在一个大的窗口的密度和温度的系统的平衡静态性能。在降低温度时，我们观察到局部有序性的逐渐增加，伴随着四配位键网络的形成。观察到三个不同的密度区域：在低密度下，系统相分离成气相和液相;在中等密度下，完全结合的颗粒的网络发展;在高密度下-由于排除体积和吸引力相互作用之间的竞争-系统形成有缺陷的网络。之前，在分子液体（如水）的非球形模型的数值研究中，以及在斑块状胶体颗粒的模型中，都观察到了同样的行为。与这些模型不同的是，为球势设计的理论处理，例如，积分方程和理想模式耦合理论的玻璃化转变，可以应用在这种情况下，开辟了道路，更深入地了解低价分子和粒子的热力学和动力学行为。
We introduce a simple spherical model whose structural properties are similar to the ones generated by models with directional interactions, by employing a binary mixture of large and small hard spheres, with a square-well attraction acting only between particles of different sizes. The small particles provide the bonds between the large ones. With a proper choice of the interaction parameters, as well as of the relative concentration of the two species, it is possible to control the effective valence. Here we focus on a specific choice of the parameters which favors tetrahedral ordering and study the equilibrium static properties of the system in a large window of densities and temperatures. Upon lowering the temperature we observe a progressive increase in local order, accompanied by the formation of a four-coordinated network of bonds. Three different density regions are observed: At low density the system phase separates into a gas and a liquid phase; at intermediate densities a network of fully bonded particles develops; at high densities--due to the competition between excluded volume and attractive interactions--the system forms a defective network. The very same behavior has been previously observed in numerical studies of nonspherical models for molecular liquids, such as water, and in models of patchy colloidal particles. Different from these models, theoretical treatments devised for spherical potentials, e.g., integral equations and ideal mode coupling theory for the glass transition, can be applied in the present case, opening the way for a deeper understanding of the thermodynamic and dynamic behavior of low valence molecules and particles.