KDI: Amorphous and Crystalline Ice Growth

由华盛顿大学化学系的Hannes Jonsson领导的一个多学科小组将对非晶冰和结晶冰的生长进行研究。该小组由美国国家科学基金会（nsf）的KDI倡议支持，并得到化学部门和极地项目办公室的资助。该项目涉及在多个时间和长度尺度上进行模拟的方法的开发和应用，以及对分子排序的大型数据集的数据挖掘。模拟将集中在冰的生长上，包括非晶和结晶，并将结合原子力显微镜、分子束和红外反射光谱的实验室实验。该项目将通过采用和进一步发展加速动力学技术，在分子水平上进行长时间尺度的模拟。一个新的半经验的相互作用势函数的水分子，基于一个极化多极膨胀，将被用来准确地表示分子间的力量在广泛的环境。长尺度模拟将通过使用分子尺度模拟的信息来开发和参数化描述介观和宏观尺度上表面形态的连续体模型来实现。需要解释的一些观测结果包括：1)随着生长过程中表面温度的升高和/或蒸汽通量的减少，从高密度非晶态冰到低密度非晶态冰再到结晶冰的转变；2)非晶冰受热时结晶冰的成核和生长；3)表面形貌随温度的变化；4)不同基质（疏水/亲水，中性/带电）对冰膜生长的影响；5)在冰中的扩散和缺陷迁移率。更好地了解冰的生长和冰的性质将对许多领域产生影响，例如，在天体物理学中，无定形的星际冰起着重要作用，在大气科学中，高层大气中结晶冰粒的成核和生长对云的形成、全球能量平衡和臭氧消耗的动力学至关重要。此外，对无定形冰的研究，可以对液态水的许多令人困惑的性质提供有价值的见解。该项目拥有一支跨学科团队，包括化学、物理和材料科学、理论和实验方面的专业知识，将采用并开发各种方法，专注于一个中心主题。由于这个多学科小组分散在五个不同的城市，因此将使用最先进的通讯技术，包括可通过万维网访问的电子笔记本和视像会议。一个紧密结合和集成的软件工具：1)系统的结构分析；2)三维图形；3)经典动力学将被开发并在万维网上提供。

A multidisciplinary group, led by Hannes Jonsson from the Chemistry Department at the University of Washington, will undertake a study of amorphous and crystalline ice growth. This group is supported through the NSF-wide KDI Initiative by a grant from the Chemistry Division and the Office of Polar Programs. The project involves the development and application of methodology for performing simulations on multiple time and length scales as well as the data mining of large data sets on molecular ordering. The simulations will focus on ice growth, both amorphous and crystalline, and will be coupled with laboratory experiments using atomic force microscopy, molecular beams and IR reflection spectroscopy. The project will involve long time scale simulations at the molecular level by employing and further developing accelerated dynamics techniques. A new semiempirical interaction potential function for water molecules, based on a polarizable multipole expansion, will be used to accurately represent the intermolecular forces in a wide range of environments. Long length scale simulations will be achieved by using information from the molecular scale simulations to develop and parameterize continuum models describing surface morphology on mesoscopic and macroscopic scales. Some of the observations to be explained include: 1) A transition from high density amorphous ice to low density amorphous ice to crystalline ice as surface temperature is increased during growth and/or vapor flux decreased; 2) nucleation and growth of crystalline ice when amorphous ice is heated; 3) variations in surface morphology with temperature; 4) effect of various substrates (hydrophobic/hydrophilic, neutral/charged) on ice film growth; and 5) diffusion and defect mobility in ice. Improved understanding of ice growth and properties of ice will have an impact in many fields, for example in astrophysics where amorphous interstellar ice plays an important role, and in atmospheric sciences where nucleation and growth of crystalline ice particles in the upper atmosphere is of central importance for cloud formation, global energy balance and dynamics of ozone depletion. Studies of amorphous ice can, furthermore, give valuable insight into the many perplexing properties of liquid water. With an interdisciplinary team including expertise in chemistry, physics and materials science, theoretical and experimental, the project will employ and develop a variety of approaches focused on one central topic. Since this multidisciplinary team is dispersed in five different cities, state of the art communication techniques will be used, including electronic notebooks accessible over the WWW and video conferencing. A software tool combining and integrating tightly: 1) systematic structure analysis; 2) 3-D graphics; and 3) classical dynamics will be developed and made available over the WWW.