Adachi Yuji, Koga Kenichiro
Graduate School of Natural Sciences, Okayama University, Okayama 700-8530, Japan.
Department of Chemistry, Okayama University, Okayama 700-8530, Japan.
J Chem Phys. 2020 Sep 21;153(11):114501. doi: 10.1063/5.0016565.
We report a molecular dynamics simulation study of dense ice modeled by the reactive force field (ReaxFF) potential, focusing on the possibility of phase changes between crystalline and plastic phases as observed in earlier simulation studies with rigid water models. It is demonstrated that the present model system exhibits phase transitions, or crossovers, among ice VII and two plastic ices with face-centered cubic (fcc) and body-centered cubic (bcc) lattice structures. The phase diagram derived from the ReaxFF potential is different from those of the rigid water models in that the bcc plastic phase lies on the high-pressure side of ice VII and does the fcc plastic phase on the low-pressure side of ice VII. The phase boundary between the fcc and bcc plastic phases on the pressure, temperature plane extends to the high-temperature region from the triple point of ice VII, fcc plastic, and bcc plastic phases. Proton hopping, i.e., delocalization of a proton, along between two neighboring oxygen atoms in dense ice is observed for the ReaxFF potential but only at pressures and temperatures both much higher than those at which ice VII-plastic ice transitions are observed.
我们报告了一项利用反应力场（ReaxFF）势对致密冰进行的分子动力学模拟研究，重点关注在早期使用刚性水模型的模拟研究中所观察到的晶体相和塑性相之间的相变可能性。结果表明，当前模型系统在冰VII与具有面心立方（fcc）和体心立方（bcc）晶格结构的两种塑性冰之间表现出相变或交叉现象。由ReaxFF势得出的相图与刚性水模型的相图不同，因为体心立方塑性相位于冰VII的高压侧，面心立方塑性相位于冰VII的低压侧。在压力 - 温度平面上，面心立方和体心立方塑性相之间的相界从冰VII、面心立方塑性相和体心立方塑性相的三相点延伸到高温区域。对于ReaxFF势，在致密冰中观察到质子在两个相邻氧原子之间跳跃，即质子离域，但仅在压力和温度都远高于观察到冰VII - 塑性冰转变的压力和温度时才会出现这种情况。
