Sato Ryuhei, Conway Lewis J, Zhang Di, Pickard Chris J, Akagi Kazuto, Sau Kartik, Li Hao, Orimo Shin-Ichi
Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Department of Materials Engineering, The University of Tokyo, Tokyo 113-8656, Japan.
Proc Natl Acad Sci U S A. 2025 Jun 3;122(22):e2413480122. doi: 10.1073/pnas.2413480122. Epub 2025 May 29.
The synthesis of new polyhydrides with high superconducting is challenging owing to the high pressures and temperatures required. In this study, we used machine-learning potential molecular dynamics simulations to investigate the initial stage of polyhydride formation in calcium hydrides. Upon contact with high-pressure H, the surface of CaH melts, leading to CaH formation. This surface melting proceeds via CaH liquid phase as an intermediate state. High pressure reduces not only the hydrogenation (CaH(s) + H(l) ↔ CaH(s)) enthalpy but also the enthalpy for liquid polyhydride formation (CaH(s) + H(l) ↔ CaH(l)). Consequently, this surface melting process becomes more favorable than the fusion of the polyhydride bulk. Thus, high pressure not only shifts the equilibrium toward the polyhydride product but also lowers the activation energy, thereby promoting the hydrogenation reaction. From these thermodynamic insights, we propose structure-search criteria for polyhydride synthesis that are both computationally effective and experimentally relevant. These criteria are based on bulk properties, such as polyhydride (product) melting temperature and pressure-dependent hydrogenation enthalpy, readily determined through supplementary calculations during structure prediction workflows.
由于所需的高压和高温，合成具有高超导性的新型多氢化物具有挑战性。在本研究中，我们使用机器学习势分子动力学模拟来研究氢化钙中多氢化物形成的初始阶段。与高压氢接触时，CaH的表面熔化，导致CaH形成。这种表面熔化通过CaH液相作为中间状态进行。高压不仅降低了氢化（CaH(s) + H(l) ↔ CaH(s)）焓，还降低了液态多氢化物形成（CaH(s) + H(l) ↔ CaH(l)）的焓。因此，这种表面熔化过程比多氢化物本体的熔化更有利。因此，高压不仅使平衡向多氢化物产物移动，还降低了活化能，从而促进了氢化反应。基于这些热力学见解，我们提出了多氢化物合成的结构搜索标准，这些标准在计算上有效且与实验相关。这些标准基于多氢化物（产物）熔化温度和压力依赖性氢化焓等体相性质，可通过结构预测工作流程中的补充计算轻松确定。
