Naden Robinson Victor, Zong Hongxiang, Ackland Graeme J, Woolman Gavin, Hermann Andreas
Centre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiantong University, Xi'an, Shanxi 710049, China
Proc Natl Acad Sci U S A. 2019 May 21;116(21):10297-10302. doi: 10.1073/pnas.1900985116. Epub 2019 Apr 11.
Various single elements form incommensurate crystal structures under pressure, where a zeolite-type "host" sublattice surrounds a "guest" sublattice comprising 1D chains of atoms. On "chain melting," diffraction peaks from the guest sublattice vanish, while those from the host remain. Diffusion of the guest atoms is expected to be confined to the channels in the host sublattice, which suggests 1D melting. Here, we present atomistic simulations of potassium to investigate this phenomenon and demonstrate that the chain-melted phase has no long-ranged order either along or between the chains. This 3D disorder provides the extensive entropy necessary to make the chain melt a true thermodynamic phase of matter, yet with the unique property that diffusion remains confined to 1D only. Calculations necessitated the development of an interatomic forcefield using machine learning, which we show fully reproduces potassium's phase diagram, including the chain-melted state and 14 known phase transitions.
各种单一元素在压力下形成不相称的晶体结构，其中沸石型“主体”亚晶格围绕着由一维原子链组成的“客体”亚晶格。在“链熔化”时，客体亚晶格的衍射峰消失，而主体的衍射峰仍然存在。客体原子的扩散预计会局限于主体亚晶格的通道中，这表明是一维熔化。在这里，我们展示了钾的原子模拟以研究这一现象，并证明链熔化相在链上或链之间都没有长程有序。这种三维无序提供了使链熔化成为物质真正热力学相所需的广泛熵，但具有扩散仅局限于一维的独特性质。计算需要使用机器学习开发一种原子间力场，我们展示了该力场能完全重现钾的相图，包括链熔化状态和14个已知的相变。
