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.

中文翻译：

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高密度冰的结构和相行为，通过具有ReaxFF势的分子动力学模拟进行。

我们报告了通过反作用力场（ReaxFF）势建模的致密冰分子动力学模拟研究，重点研究了在早期使用刚性水模型进行的模拟研究中观察到的结晶相和塑性相之间相变的可能性。结果表明，本模型系统在VII型冰和两个具有面心立方（fcc）和体心立方（bcc）晶格结构的塑料冰中表现出相变或交叉。从ReaxFF势得出的相图与刚性水模型的相图不同，因为bcc塑性相位于冰VII的高压侧，而fcc塑性相位于冰VII的低压侧。fcc和bcc塑性相之间的相界取决于压力，温度平面从VII，FCC和BCC塑性相的三相延伸到高温区域。对于ReaxFF电位，在致密冰中两个相邻的氧原子之间存在质子跳变，即质子的离域，但只有在压力和温度都比观察到的VII-冰塑性冰转变高的压力和温度下才能观察到。