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无定形和结晶冰的生长进行研究。 该小组通过NSF范围内的KDI倡议得到化学部和极地项目办公室的资助。 该项目涉及开发和应用在多个时间和长度尺度上进行模拟的方法，以及对分子排序的大型数据集进行数据挖掘。 模拟将侧重于冰的生长，包括无定形和结晶，并将与使用原子力显微镜，分子束和红外反射光谱的实验室实验相结合。 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。 一个新的半经验的水分子相互作用势函数，基于极化多极展开，将被用来准确地表示在广泛的环境中的分子间的力量。 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的表面形态的连续模型来实现。 其中的一些观察结果包括：（1）随着生长过程中表面温度的升高和/或水汽通量的降低，从高密度无定形冰到低密度无定形冰再到结晶冰的转变;（2）当无定形冰被加热时结晶冰的成核和生长;（3）表面形态随温度的变化; 4）不同基质（疏水/亲水、中性/带电）对冰膜生长的影响; 5）冰中的扩散和缺陷迁移率。 增进对冰的生长和冰的特性的了解将对许多领域产生影响，例如在天体物理学中，无定形星际冰发挥着重要作用;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、全球能源平衡和臭氧消耗的动态具有核心重要性。 此外，对无定形冰的研究可以为了解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，该项目将采用和开发各种方法，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，将使用最先进的通信技术，包括通过万维网和电视会议访问的电子笔记本。 将开发一个将1）系统结构分析; 2）三维图形; 3）经典动力学紧密结合的软件工具，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.