Two kinds of potential surfaces for supercooled water and percolation transition

本计画涵盖了水在整体与封闭状态下的相态行为。(1)本文报道了分子动力学（MD）方法对体相水在过冷状态下的相变过程的模拟。通过考察水分子的局部结构、氢键数分布等，研究了水分子的压缩和减压循环。(2)我们已经报道了MD证据表明一种新型的一阶相变-液体到双层无定形转变-高于大气压下散装水的冻结温度。当两层水被限制在宽度小于1纳米的疏水狭缝孔中时，这种多晶相变唯一出现。在冷却时，具有不完美的随机氢键网络的受限水经历到双层无定形的过渡，该双层无定形由于形成各种氢键多边形而具有完美的网络，但没有长程有序。这种转变是可视化的，并检查了相关的热力学性质。该转变与四面体配位的物质，如液态硅，液态碳和液态磷中观察到的一些特征相同。(3)我们已经报道了分子动力学模拟的证据相行为的封装水形成的新相的准一维冰和存在的固-液临界点。我们发现，在狭窄的碳纳米管中，水可以冻结成七边形，六边形，五边形或正方形的冰纳米管，这取决于碳纳米管的直径（1-1.4 nm）和所施加的轴向压力。基于树能量计算，我们评估了实验条件下，散装液态水可以封装到碳纳米管，可以转化为冰纳米管。

The present project covers phase behaviors of water in bulk and confined states.(1) We have reported molecular dynamics (MD) simulations of bulk water in supercooled state and the associated liquid-liquid phase transition. This has been investigated by examining local structure of individual water molecules, the hydrogen bond number distribution etc. Also examined is compression and decompression cycle at temperature 0 K.(2) We have reported MD evidence suggesting a new type of first-order phase transition - a liquid-to-bilayer amorphous transition --- above the freezing temperature of bulk water under atmospheric pressure. This polyamorphic phase transition appears uniquely when a two-layer water is confined in a hydrophobic slit pore at a width of less than one nanometer. Upon cooling, the confined water which has an imperfect random hydrogen-bonded network undergoes the transition to a bilayer amorphous which has a perfect network due to the formation of various hydrogen-bonded polygons yet has no long-range order. This transition was visualized and the associated thermodynamic properties were examined The transition shares some characteristics with those observed in tetrahedrally coordinated substances such as liquid silicon, liquid carbon and liquid phosphorus.(3) We have reported MD simulation evidence of phase behavior of encapsulated water-formation of new phases of quasi-one-dimensional ice and existence of a solid-liquid critical point. We discover that in narrow carbon nanotubes water can freeze into heptagonal, hexagonal, pentagonal, or square ice nanotubes, depending on the diameter of carbon nanotubes (1-1.4 nm) and the applied axial pressure as well. Based on the tree energy calculation, we assessed experimental conditions under which bulk liquid water can be encapsulated into carbon nanotubes and can be transformed into ice nanotubes.