超低密度三维晶体负压冰的结构预测、相图计算和应用探索

New phases of crystalline ice with ultralow density under negative pressure is a new topic of the studies on water. Few studies on ices under negative pressure has been reported until now. In this project, a multi-scale simulation scheme is proposed on the studies of crystalline ices under negative pressure. A large amount of crystalline ice candidates under negative pressure will be constructed, a part of which will be screened based on their stabilities from first-principles calculations and molecular dynamics simulations. A new phase diagram of water under negative pressure will be constructed, in which the new phases from our prediction will be included. Based on the experiences on the predictions of new crystalline ices from water molecules or water bubble clusters, a self-assembly mechanism would be revealed, which could be used in the predictions of new crystal phases of other molecular crystal materials and other clathrate or porous materials. In addition, crystalline ices under negative pressure can be used to store hydrogen, methane and other hydrocarbon molecules employing their unique clathrate framework, a new record of the hydrogen storage capacity in solid materials would be set by the new predicted phases with ultralow density. CO2, SO2, H2S and other toxic gas also can be sealed in the ices under negative pressure, which could be used to improve the air quality by reducing the amount of CO2 and toxic gases in atmosphere. The phase diagram of water under negative pressure will be rich and expanded to lower negative pressure region through this project. At the same time, the knowledge of people about water will be expanded. The fields about ices under negative pressure would be led by Chinese researchers in future if we got this funding.

负压冰是水科学研究领域一个新分支，目前为止，全世界对负压冰的研究寥寥无几。本项目提出采用多尺度计算机模拟方案，对可能的超低密度负压冰相进行高通量的搜索，结合第一性原理计算和分子动力学模拟，筛选出可能稳定存在的负压冰相，把其存在的温度压力区间定量地表征在相图上。基于负压冰的构建经验，探索其中暗含的水分子或水分子团簇构造固相的自组装机制，试图把这种机制应用到其他分子晶体材料或笼形物及多孔型材料的固体新相预测。另外，利用负压冰中独特的笼状空穴，储存氢气及甲烷等能源气体，试图刷新氢气在负压冰乃至固体材料中的储量记录；封存二氧化碳或二氧化硫、硫化氢等有毒气体，试图探索其在大气治理中应用的可行性，帮助提高空气质量。这项工作将丰富冰在负压下的相图，使水的相图拓展到更低的负压区，进一步拓展人类对水的认知。本项目的开展将会使我国在负压冰的研究领域占据先机，强占世界领先地位，领导水科学研究的这一新分支。

负压冰是水科学研究领域一个新分支，目前为止，全世界对负压冰的研究寥寥无几。本项目采用多尺度的计算机模拟方案，对可能稳定存在的超低密度负压冰相进行大量搜索，结合第一性原理计算和分子动力学模拟，筛选出了一个亚稳负压冰新相sL和两个可以在水的温度压力相图上出现的超低密度新相EMT和FAU，它们的密度为0.5克每立方厘米（目前为止，密度最小的三维固体冰相），重新绘制了水的负压相图。同时，通过我们的模拟研究发现，EMT负压冰相是优异的储氢材料，其储氢量可以高达12.9 wt%，将近美国能源部2020年固体材料储氢量目标值（4.5 wt%）的3倍。本项目的研究结果，不仅丰富了冰的结构相，拓展了水的相图，进一步扩展了人类对于水的认知，而且提供了一种新的有潜力的储氢方式，如果本项目中预测的负压冰相被实验科学家合成出来，并成功进行储氢应用，将会造福社会和人类，为国家带来直接的经济价值。此外，本项目的研究，证明了通过对已知同类型结构的骨架原子替代构建冰的新相，然后结合第一性原理计算和分子动力学模拟筛选，是一种高效且可行的预测冰的新相的方法，将来可以扩展到其他种类材料新相的预测研究。