Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125.
Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125
Proc Natl Acad Sci U S A. 2019 Feb 5;116(6):1998-2003. doi: 10.1073/pnas.1817383116. Epub 2019 Jan 24.
We developed the RexPoN force field for water based entirely on quantum mechanics. It predicts the properties of water extremely accurately, with = 273.3 K (273.15 K) and properties at 298 K: ΔH = 10.36 kcal/mol (10.52), density = 0.9965 g/cm (0.9965), entropy = 68.4 J/mol/K (69.9), and dielectric constant = 76.1 (78.4), where experimental values are in parentheses. Upon heating from 0.0 K (ice) to 273.0 K (still ice), the average number of strong hydrogen bonds (SHBs, r ≤ 2.93 Å) decreases from 4.0 to 3.3, but upon melting at 273.5 K, the number of SHBs drops suddenly to 2.3, decreasing slowly to 2.1 at 298 K and 1.6 at 400 K. The lifetime of the SHBs is 90.3 fs at 298 K, increasing monotonically for lower temperature. These SHBs connect to form multibranched polymer chains (151 HO per chain at 298 K), where branch points have 3 SHBs and termination points have 1 SHB. This dynamic fluctuating branched polymer view of water provides a dramatically modified paradigm for understanding the properties of water. It may explain the 20-nm angular correlation lengths at 298 K and the critical point at 227 K in supercooled water. Indeed, the 15% jump in the SHB lifetime at 227 K suggests that the supercooled critical point may correspond to a phase transition temperature of the dynamic polymer structure. This paradigm for water could have a significant impact on the properties for protein, DNA, and other materials in aqueous media.
我们完全基于量子力学为水开发了 RexPoN 力场。它可以非常准确地预测水的性质，其中 = 273.3 K（273.15 K）和 298 K 时的性质为：ΔH = 10.36 kcal/mol（10.52），密度 = 0.9965 g/cm（0.9965），熵 = 68.4 J/mol/K（69.9），介电常数 = 76.1（78.4），括号内为实验值。从 0.0 K（冰）加热到 273.0 K（仍是冰）时，平均氢键数量（r ≤ 2.93 Å）从 4.0 个减少到 3.3 个，但在 273.5 K 时熔化时，氢键数量突然减少到 2.3 个，在 298 K 时缓慢减少到 2.1 个，在 400 K 时减少到 1.6 个。298 K 时氢键的寿命为 90.3 fs，随着温度降低呈单调增加。这些氢键连接形成多分支聚合物链（298 K 时每链有 151 个 HO），其中分支点有 3 个氢键，末端点有 1 个氢键。这种动态波动的分支聚合物水观点为理解水的性质提供了一个显著改进的范例。它可能解释了 298 K 时 20nm 的角相关长度和过冷水中 227 K 的临界点。实际上，227 K 时氢键寿命增加 15%表明过冷临界点可能对应于动态聚合物结构的相变温度。这种水的范例可能会对蛋白质、DNA 和其他水介质中的材料的性质产生重大影响。
