Dehydration of hydrous minerals is the key for understanding the partial melting and earthquakes taking place at subduction zones. It has been reported that a large amount of H2O defects (HD) can be formed during the dehydration process. However, the HD effects on the properties of hydrous minerals have never been considered previously. In this work, density functional theory (DFT) calculations were carried out to study the formation enthalpies of HD in lizardite. The calculated formation enthalpies of lizardite with 0.8125 wt% HD are below 0.5 eV at pressures from 0 to 7 GPa, which are low enough for the formation of HD, especially at high temperature. The presence of HD exerts significant influence on the elastic property of lizardite, resulting in lower seismic velocities and obviously higher seismic velocity anisotropy. We also calculated the migration barrier energy of H+, Mg2+, and Si4+ in lizardite. H+ migration barrier energy is 1.16 eV (vertical with ‹001› direction) and 3.40 eV (along ‹001› direction) at the pressure of 3 GPa, while Mg and Si present much higher values of more than 5 and 9 eV, respectively. Further simulations of first-principles molecular dynamics (FPMD) on lizardite with and without HD indicate that the crystal structure of HD-bearing lizardite is thermodynamically stable, and proton conduction is not obvious in lizardite and HD-bearing lizardite at temperatures below 900 K and pressures below 2 GPa.

中文翻译：

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蜥蜴石中H2O缺陷形成对弹性性能影响的第一性原理研究

含水矿物的脱水是理解俯冲带部分熔融和地震的关键。据报道，在脱水过程中会形成大量的 H2O 缺陷 (HD)。然而，以前从未考虑过 HD 对含水矿物特性的影响。在这项工作中，进行了密度泛函理论 (DFT) 计算以研究蜥蜴石中 HD 的形成焓。在 0 到 7 GPa 的压力下，计算出的含 0.8125 wt% HD 的蜥蜴石的形成焓低于 0.5 eV，这对于 HD 的形成来说足够低，尤其是在高温下。HD的存在对蜥蜴岩的弹性性质有显着影响，导致地震速度降低，地震速度各向异性明显升高。我们还计算了蜥蜴石中 H+、Mg2+ 和 Si4+ 的迁移势垒能。在 3 GPa 的压力下，H+ 迁移势垒能量为 1.16 eV（与 ‹001› 方向垂直）和 3.40 eV（沿 ‹001›方向），而 Mg 和 Si 的值分别高于 5 和 9 eV。对含 HD 和不含 HD 的蜥蜴石进行第一性原理分子动力学 (FPMD) 的进一步模拟表明，含 HD 蜥蜴石的晶体结构热力学稳定，在温度低于 900 K 和含 HD 蜥蜴石中，质子传导不明显。压力低于 2 GPa。而 Mg 和 Si 的值分别高于 5 和 9 eV。对含 HD 和不含 HD 的蜥蜴石进行第一性原理分子动力学 (FPMD) 的进一步模拟表明，含 HD 的蜥蜴石的晶体结构热力学稳定，在温度低于 900 K 和含 HD 的蜥蜴石中，质子传导不明显。压力低于 2 GPa。而 Mg 和 Si 的值分别高于 5 和 9 eV。对含 HD 和不含 HD 的蜥蜴石进行第一性原理分子动力学 (FPMD) 的进一步模拟表明，含 HD 蜥蜴石的晶体结构热力学稳定，在温度低于 900 K 和含 HD 蜥蜴石中，质子传导不明显。压力低于 2 GPa。