发表机构
Seoul National University; Ajou University（首尔大学; 亚洲大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过环聚合物分子动力学模拟发现，核量子效应通过加速氨分子的锥形反转，在低于210 K时增强过冷氨中的扩散，170 K时扩散增强达18%，并伴随氢键配位和局部密度瞬态降低。
AI 中文摘要
在液态氨中，可用氢键供体位点与受体位点之间的不平衡限制了类似水的四面体连接，导致在致密液体中形成稀疏且短暂的关联。我们探究了量子敏感性的局部重排是否仍能对这种弱连接液体中的扩散产生显著贡献。我们使用基于r$^2$SCAN训练的机器学习力场，在170至250 K温度范围内比较了经典和热浴环聚合物分子动力学模拟。氨的分子几何结构可以随氮原子穿过三个氢原子所在平面而改变，这一运动被称为锥形反转。核量子效应增加了反转速率并降低了其表观活化能。反转事件伴随着第一溶剂化壳层内氢键配位和局部密度的瞬态降低。尽管核量子效应在整个研究温度范围内降低了密度和粘度，但在较温暖的液体中扩散仅受到微弱影响。量子增强的扩散在约210 K以下出现，并在170 K时达到18%，与笼逃逸的增强相对应。这些观察结果支持一种反转辅助的扩散机制，其中空间局域化的、量子敏感的内部运动与笼弛豫耦合，而无需持久的四面体网络。
英文摘要
In liquid ammonia, an imbalance between available hydrogen-bond donor and acceptor sites limits water-like tetrahedral connectivity, leaving sparse and short-lived associations within a densely packed liquid. We ask whether quantum-sensitive local rearrangements can nevertheless contribute appreciably to diffusion in this weakly connected liquid. We compare classical and thermostatted ring polymer molecular dynamics from 170 to 250 K using an r$^2$SCAN-trained machine learning force field. Ammonia can change its molecular geometry as the nitrogen atom passes through the plane of the three hydrogen atoms, a motion known as pyramidal inversion. Nuclear quantum effects increase the inversion rate and reduce its apparent activation energy. Inversion events are accompanied by transient reductions in hydrogen-bond coordination and local density within the first solvation shell. Although nuclear quantum effects lower density and viscosity throughout the studied range, diffusion remains only weakly affected in the warmer liquid. The quantum enhancement of diffusion emerges below approximately 210 K and reaches 18% at 170 K, tracking the enhancement of cage escape. These observations support an inversion-assisted contribution to diffusion, in which a spatially localized, quantum-sensitive internal motion couples to cage relaxation without a persistent tetrahedral network.
Comments37 pages, 13 figures
