Thermodynamic Stability of Ice II and Its Hydrogen-Disordered Counterpart: Role of Zero-Point Energy
Thermodynamic Stability of Ice II and Its Hydrogen-Disordered Counterpart: Role of Zero-Point Energy
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DOI：
10.1021/acs.jpcb.5b09544
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发表时间：
2016-03-03
影响因子：
3.3
通讯作者：
Tanaka, Hideki
中科院分区：
文献类型：
--
作者：
Nakamura, Tatsuya;Matsumoto, Masakazu;Tanaka, Hideki
我们调查为什么没有氢无序形式的冰II已被发现在自然界中，尽管事实上，大多数氢有序的冰有氢无序的对应物。从理论上评估了一组氢有序冰II变体相对于冰II的热力学稳定性。结果发现，冰II是更稳定的比无序的变体，从而产生满足简单的冰规则，由于较低的零点能以及对相互作用能。随着温度的升高，无序冰II相的剩余熵逐渐补偿不利的自由能。然而，这种交叉发生在远高于冰III熔点的高温下。因此，自然界中不存在氢无序相。部分氢无序冰的热力学稳定性也仔细检查通过检查自由能组件的几个变种获得系统的反转冰II中的OH方向。一种变体的势能低于冰II结构的势能，但由于零点能，其吉布斯自由能略高于冰II。热力学稳定性的微小差异留下了真实的冰II中部分氢无序的可能性。
We investigate why no hydrogen-disordered form of ice II has been found in nature despite the fact that most of hydrogen-ordered ices have hydrogen-disordered counterparts. The thermodynamic stability of a set of hydrogen-ordered ice II variants relative to ice II is evaluated theoretically. It is found that ice II is more stable than the disordered variants so generated as to satisfy the simple ice rule due to the lower zero point energy as well as the pair interaction energy. The residual entropy of the disordered ice II phase gradually compensates the unfavorable free energy with increasing temperature. The crossover, however, occurs at a high temperature well above the melting point of ice III. Consequently, the hydrogen-disordered phase does not exist in nature. The thermodynamic stability of partially hydrogen-disordered ices is also scrutinized by examining the free-energy components of several variants obtained by systematic inversion of OH directions in ice II. The potential energy of one variant is lower than that of the ice II structure, but its Gibbs free energy is slightly higher than that of ice II due to the zero-point energy. The slight difference in the thermodynamic stability leaves the possibility of the partial hydrogen-disorder in real ice II.