Center for Materials Simulations and Design, Graduate School of Energy, Environment, Water, and Sustainability, World Class University, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea.
Proc Natl Acad Sci U S A. 2011 Sep 13;108(37):15101-5. doi: 10.1073/pnas.1110322108. Epub 2011 Aug 25.
We recently developed the electron force field (eFF) method for practical nonadiabatic electron dynamics simulations of materials under extreme conditions and showed that it gave an excellent description of the shock thermodynamics of hydrogen from molecules to atoms to plasma, as well as the electron dynamics of the Auger decay in diamondoids following core electron ionization. Here we apply eFF to the shock thermodynamics of lithium metal, where we find two distinct consecutive phase changes that manifest themselves as a kink in the shock Hugoniot, previously observed experimentally, but not explained. Analyzing the atomic distribution functions, we establish that the first phase transition corresponds to (i) an fcc-to-cI16 phase transition that was observed previously in diamond anvil cell experiments at low temperature and (ii) a second phase transition that corresponds to the formation of a new amorphous phase (amor) of lithium that is distinct from normal molten lithium. The amorphous phase has enhanced valence electron-nucleus interactions due to localization of electrons into interstitial locations, along with a random connectivity distribution function. This indicates that eFF can characterize and compute the relative stability of states of matter under extreme conditions (e.g., warm dense matter).
我们最近开发了电子力场（eFF）方法，用于在极端条件下对材料的非绝热电子动力学进行实际模拟，结果表明，它可以极好地描述从分子到原子再到等离子体的氢的冲击热力学，以及在金刚石烷中核心电子电离后，俄歇衰变的电子动力学。在这里，我们将 eFF 应用于锂金属的冲击热力学，发现了两个截然不同的连续相变，它们表现为冲击 Hugoniot 中的拐点，这是以前在实验中观察到的，但没有得到解释。通过分析原子分布函数，我们确定了第一个相变对应于（i）先前在低温下的金刚石压腔实验中观察到的 fcc 到 cI16 相变，以及（ii）对应于新的非晶相（amor）形成的第二个相变锂，它与正常熔融锂不同。非晶相由于电子局域到间隙位置，增强了价电子-核相互作用，同时具有随机连接分布函数。这表明 eFF 可以表征和计算极端条件下（例如，温稠密物质）物质状态的相对稳定性。
