KDI: Amorphous and Crystalline Ice Growth

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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.