Bertolazzo Andressa A, Kumar Abhinaw, Chakravarty Charusita, Molinero Valeria
Department of Chemistry, The University of Utah , Salt Lake City, Utah 84112-0850, United States.
Department of Chemistry, Indian Institute of Technology-Delhi , New Delhi 110016, India.
J Phys Chem B. 2016 Mar 3;120(8):1649-59. doi: 10.1021/acs.jpcb.5b08432. Epub 2015 Oct 12.
Water, silicon, silica, and other liquids that favor tetrahedral order display thermodynamic, dynamic, and structural anomalies in the pressure range in which they form tetrahedrally coordinated crystals. The tetrahedral order in these liquids is induced by anisotropic hydrogen bonding or covalent interactions, or, in ionic melts, by an appropriate size ratio of the ions. Simple isotropic two-length scale models have been extensively used to understand the origin of anomalies in complex liquids. However, single-component isotropic liquids characterized to date generally do not stabilize tetrahedral crystals, and in the few cases that they do, it was found that the liquids do not display anomalies in the region of the tetrahedral crystal. This poses the question of whether it is possible for isotropic pair potentials to display water-like phase behavior and anomalies. In this work, we use molecular dynamics simulations to investigate the phase behavior and the existence and loci of anomalies of a single-component purely repulsive isotropic pair potential that stabilizes diamond in the ground state over a wide range of pressures. We demonstrate that, akin to water, silica, and silicon, the isotropic potential of Marcotte, Stillinger, and Torquato (MST) presents structural, dynamic, and thermodynamic anomalies in the region of stability of the tetrahedral crystal. The regions of anomalies of MST are nested in the T-p plane following the same hierarchy as in silica: the region of diffusional anomalies encloses the region of structural anomalies, which in turn contains the region of thermodynamic anomalies. To our knowledge, MST is the first example of pair potential for which water-like anomalies are associated with the formation of tetrahedral order.
水、硅、二氧化硅以及其他有利于四面体有序排列的液体，在形成四面体配位晶体的压力范围内会表现出热力学、动力学和结构异常。这些液体中的四面体有序排列是由各向异性氢键或共价相互作用诱导产生的，或者在离子熔体中，是由离子的适当尺寸比诱导产生的。简单的各向同性双长度尺度模型已被广泛用于理解复杂液体中异常现象的起源。然而，迄今为止所表征的单组分各向同性液体通常不会使四面体晶体稳定，并且在少数能使四面体晶体稳定的情况下，发现这些液体在四面体晶体区域内并未表现出异常现象。这就提出了一个问题，即各向同性对势是否有可能表现出水样的相行为和异常现象。在这项工作中，我们使用分子动力学模拟来研究一种单组分纯排斥各向同性对势的相行为以及异常现象的存在和位置，该对势在很宽的压力范围内能使基态的金刚石稳定。我们证明，与水、二氧化硅和硅类似，马尔科特、斯蒂林格和托尔夸托（MST）的各向同性势在四面体晶体的稳定区域内呈现出结构、动力学和热力学异常现象。MST异常区域在T - p平面内嵌套的层次结构与二氧化硅中的相同：扩散异常区域包围结构异常区域，而结构异常区域又包含热力学异常区域。据我们所知，MST是第一个其水样异常现象与四面体有序排列形成相关的对势实例。
