超冷极性气体中单个离子的自限电致伸缩：从介观离子到结晶分子环
Self-limiting electrostriction of a single ion in an ultracold polar gas: From mesoscopic ions to crystalline molecular rings
AI总结：
该研究探究超冷极性气体中单个离子周围极性分子的自组装，结合全局优化与扩散蒙特卡洛方法，揭示了离子结合极性分子团簇的特殊结构与稳定性，为研究量子浴中带电杂质提供新途径。
AI中文摘要：
我们研究了浸没在超冷、稀薄二维分子气体中的单个离子周围极性分子的自组装过程。离子通过电荷-偶极相互作用使分子取向并吸引分子，在杂质周围产生强电致伸缩积累，而分子间排斥作用限制了进一步的致密化，有利于形成空间延展的构型。我们将全局优化与扩散蒙特卡洛（diffusion Monte Carlo）方法结合，计算了与离子结合的分子数作为函数的蒸发能。与常规带电团簇和范德瓦尔斯团簇不同，蒸发能对团簇尺寸呈现类平台依赖关系，反映了同心分子环的依次形成。这些结构由离子电场的拓扑结构以及吸引性的离子-分子相互作用、排斥性的环内相互作用与相邻环间吸引性关联之间的竞争所决定，而非由常规配位或二十面体堆积决定。在弱相互作用区域，形成的结构为延展的介观分子离子；而在更强的相互作用下，则产生愈发刚性的类晶体分子环。我们进一步分析了它们对热扰动、随时间变化的离子阱的稳定性，发现大量团簇在实验相关条件下仍保持稳定。分子间排斥与偶极几何还抑制了近距离的离子-分子遭遇，暗示存在一种本征屏蔽机制。我们的结果确立了离子结合的极性分子团簇为一类独特的介观分子离子，并为研究具有各向异性相互作用的量子浴中的带电杂质开辟了途径。
英文摘要：
We investigate the self-assembly of polar molecules around a single ion immersed in an ultracold, dilute two-dimensional molecular gas. The ion aligns and attracts the molecules through charge-dipole interactions, producing a strong electrostrictive accumulation around the impurity, while intermolecular repulsion limits further densification and favors spatially extended configurations. By combining global optimization with diffusion Monte Carlo, we calculate the evaporation energy as a function of the number of molecules bound to the ion. In contrast to conventional charged and van der Waals clusters, the evaporation energy exhibits a plateau-like dependence on cluster size, reflecting the sequential formation of concentric molecular rings. These structures are governed by the topology of the ion's electric field and by the competition between attractive ion-molecule interactions, repulsive intra-ring interactions, and attractive correlations between neighboring rings, rather than by conventional coordination or icosahedral packing. In the weak-interaction regime, the resulting structures form extended mesoscopic molecular ions, whereas stronger interactions produce increasingly rigid, crystal-like molecular rings. We further analyze their stability against thermal perturbations and the time-dependent ion trap and find that a broad range of clusters remain stable under experimentally relevant conditions. The intermolecular repulsion and dipolar geometry also suppress close-range ion-molecule encounters, suggesting an intrinsic shielding mechanism. Our results establish ion-bound polar-molecule clusters as a distinct class of mesoscopic molecular ions and open a route to studying charged impurities in quantum baths with anisotropic interactions.
