Skarmoutsos Ioannis, Samios Jannis, Guardia Elvira
Laboratory of Physical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece.
Department of Chemistry, Laboratory of Physical Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis 157-71, Athens, Greece.
J Phys Chem Lett. 2022 Aug 25;13(33):7636-7644. doi: 10.1021/acs.jpclett.2c01477. Epub 2022 Aug 11.
Using molecular dynamics simulations in combination with the two-phase thermodynamic model, we reveal novel characteristic fingerprints of the crossing of the Frenkel and melting line on the properties of high-pressure water at a near-critical temperature (1.03). The crossing of the Frenkel line at about 1.17 GPa is characterized by a crossover in the rotational and translational entropy ratio /, indicating a change in the coupling between translational and rotational motions which is also reflected in the shape of the rotational density of states. The observed isosbestic points in the translational and rotational density of states are also blue-shifted at density and pressure conditions higher than the ones corresponding to the Frenkel line. The first-order phase transition from a rigid liquid to a face-centered cubic plastic crystal phase at about 8.5 GPa is reflected in the discontinuous changes in the translational and rotational entropy, particularly in the significant increase of the ratio /. A noticeable discontinuous increase of the dielectric constant has also been revealed when crossing this melting line, which is attributed to the different arrangement of the water molecules in the plastic crystal phase. The reorientational dynamics in the plastic crystal phase is faster in comparison with the "rigid" liquid-like phase, but it remains unchanged upon a further pressure increase in the range of 8.5-11 GPa.
结合分子动力学模拟和两相热力学模型，我们揭示了在近临界温度（1.03）下，高压水在弗伦克尔线和熔点线交叉时，其性质所呈现的新特征指纹。在约1.17 GPa处弗伦克尔线的交叉表现为转动熵与平动熵之比/的交叉，这表明平动和转动运动之间的耦合发生了变化，这也反映在转动态密度的形状上。在高于对应弗伦克尔线的密度和压力条件下，平动和转动态密度中观察到的等吸收点也发生了蓝移。在约8.5 GPa处从刚性液体到面心立方塑性晶体相的一级相变反映在平动和转动熵的不连续变化中，特别是在比值/的显著增加上。当越过这条熔点线时，还揭示了介电常数明显的不连续增加，这归因于塑性晶体相中水分子的不同排列。与“刚性”类液相相比，塑性晶体相中的重取向动力学更快，但在8.5 - 11 GPa范围内进一步增加压力时，它保持不变。
