Hydrogen-Bond Symmetrization of δ-AlOOH

The 6-AIOOH can transport water into the deep mantle along cold subducting slab geotherm. We investigate the hydrogen-bond symmetrization behavior of 6-AIOOH under the relevant pressure-temperature condition of the lower mantle using ab initio molecular dynamics （MD）. The static symmetrization pressure of 30.0 GPa can be reduced to 17.0 GPa at 30014 by finite-temperature （T） statistics, closer to the experimental observation of ~10.0 GPa. The symmetrization pressure obtained by MD simulation is related to T by P （GPa） = 13.9 （GPa） ＋ 0.01 （GPa/K） x T （K）. We conclude that 6-AIOOH in the lower mantle exists with symmetric hydrogen bond from its birthplace, or someplace slightly deeper, to the core-mantle boundary （CM13） along cold subducting slab geotherm, The bulk modulus decreases with T and increases anomalously upon symmetrization： Ko （GPa） = 181 （GPa） - 0,013 （GPa/K） x T （K） for 6-AIOOH with asymmetric hydrogen bond, and Ko （OPa） = 216 （GPa） - 0.013 （GPa/K） × T （K） for 6-AIOOH with symmetric hydrogen bond. Our results provide an important insight into the existent form and properties of 6-AIOOH in the lower mantle.

Discriminating High-Pressure Water Phases Using Rare-Event Determined Ionic Dynamical Properties

Recent discoveries of dynamic ice Ⅶ and superionic ice highlight the importance of ionic diffusions in discriminating high-pressure(P) water phases.The rare event nature and the chemical bond breaking associated with these diffusions,however,make extensive simulations of these processes unpractical to ab initio and inappropriate for force field based methods.Using a first-principles neural network potential,we performed a theoretical study of water at 5-70 GPa and 300-3000 K.Long-time dynamics of protons and oxygens were found indispensable in discriminating several subtle states of water,characterized by proton’s and oxygen ion’s diffusion coefficients and the distribution of proton’s displacements.Within dynamic ice Ⅶ,two types of proton transfer mechanisms,i.e.,translational and rotational transfers,were identified to discriminate this region further into dynamic ice Ⅶ T and dynamic ice Ⅶ R.The triple point between ice Ⅶ,superlonic ice(SI),and liquid exists because the loosening of the bee oxygen skeleton is prevented by the decrease of interatomic distances at high P’s.The melting of ice Ⅶ above ~40 GPa can be understood as a process of two individual steps:the melting of protons and the retarded melting of oxygens,responsible for the forming of SI.The boundary of the dynamic ice VIF and SI lies on the continuation line ice Ⅶ’s melting curve at low P’s.Based on these,a detailed phase diagram is given,which may shed light on studies of water under P’s in a wide range of interdisciplinary sciences.

物质的态与相

在现代物理学研究中,物质的态与相扮演着重要的角色。它们之间既有联系,又有形成时间的不同以及具体涵义的差异。文章把两个概念的认识过程分为三个阶段:(1)贯穿整个19世纪的第一阶段,主题大致可归结为“态与相概念的先后提出”,将围绕当时人们在描述物质存在形式时“从理想气体的克拉珀龙方程到真实体系的范德瓦耳斯模型”展开。