Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588.
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588;
Proc Natl Acad Sci U S A. 2018 Oct 9;115(41):10263-10268. doi: 10.1073/pnas.1809198115. Epub 2018 Sep 24.
Both carbon dioxide (CO) and water (HO) are triatomic molecules that are ubiquitous in nature, and both are among the five most abundant gases in the Earth's atmosphere. At low temperature and ambient pressure, both CO and HO form molecular crystals--dry ice I and ice I Because water possesses distinctive hydrogen bonds, it exhibits intricate and highly pressure-dependent phase behavior, including at least 17 crystalline ice phases and three amorphous ice phases. In contrast, due to its weak van der Waals intermolecular interactions, CO exhibits fewer crystalline phases except at extremely high pressures, where nonmolecular ordered structures arise. Herein, we show the molecular dynamics simulation results of numerous 2D polymorphs of CO molecules in slit nanopores. Unlike bulk polymorphs of CO, 2D CO polymorphs exhibit myriad crystalline and amorphous structures, showing remarkable polymorphism and polyamorphism. We also show that depending on the thermodynamic path, 2D solid-to-solid phase transitions can give rise to previously unreported structures, e.g., wave-like amorphous CO structures. Our simulation also suggests intriguing structural connections between 2D and 3D dry ice phases (e.g., and PA-3) and offers insights into CO polyamorphic transitions through intermediate liquid or amorphous phases.
二氧化碳（CO）和水（HO）都是三原子分子，在自然界中无处不在，并且都是地球大气中含量最丰富的五种气体之一。在低温和环境压力下，CO 和 HO 都形成分子晶体——干冰 I 和冰 I。由于水具有独特的氢键，因此它表现出复杂且高度依赖压力的相行为，包括至少 17 种晶相和 3 种非晶相。相比之下，由于其较弱的范德华分子间相互作用，CO 除了在极高压力下会出现非分子有序结构外，呈现出的结晶相较少。在此，我们展示了在狭缝纳米孔中 CO 分子的许多二维多晶型体的分子动力学模拟结果。与 CO 的体相多晶型体不同，二维 CO 多晶型体表现出多种晶态和非晶态结构，表现出显著的多晶型性和多型性。我们还表明，根据热力学路径，二维固-固相变可以产生以前未报道过的结构，例如，具有波浪状的非晶 CO 结构。我们的模拟还揭示了二维和三维干冰相（例如，和 PA-3）之间有趣的结构联系，并通过中间液体或非晶相提供了对 CO 多型性转变的深入了解。
