AI 中文总结
该研究通过实验与模拟发现立方冰I$_c$在70 K附近有密度最大值，其负热膨胀源于氢键网络的集体量子效应，由核统计与氢键动力学主导。
AI 中文摘要
我们报告了通过C2氢水合物的拓扑脱气制备的无堆垛无序立方冰I$_c$的中子粉末衍射测量和路径积分分子动力学模拟。在低温稳定范围内，冰I$_c$在70 K附近表现出密度最大值，尽管其长程堆垛序列与六方冰I$_h$不同，但与六方冰I$_h$的密度最大值非常吻合。因此，冰I中的负热膨胀并非六方堆垛所特有，而是源于其共同的开放四面体氢键网络。仅当包含核量子效应时，采用MB-pol势的模拟才能定量重现实验中的异常现象。在温度分辨率范围内，密度最大值与质子量子分布的各向异性最大值重合。中子测得的位移参数独立显示质子的横向位移显著增强，而声子计算则确定了具有最负格林艾森参数的低频横向模式。这些结果共同证实，冰I的负热膨胀是由核统计和氢键网络动力学主导的集体量子效应。
英文摘要
We report neutron powder diffraction measurements and path-integral molecular dynamics simulations of stacking-disorder-free cubic ice I$_c$, produced by topotactic degassing of C2 hydrogen hydrate. Across the cryogenic stability range, ice I$_c$ exhibits a density maximum near 70 K, closely matching that of hexagonal ice I$_h$ despite their different long-range stacking sequences. Negative thermal expansion in ice I is therefore not specific to hexagonal stacking, but arises from the shared open tetrahedral hydrogen-bond network. Simulations with the MB-pol potential quantitatively reproduce the experimental anomaly only when nuclear quantum effects are included. The density maximum coincides, within the temperature resolution, with maximal anisotropy of the proton quantum distribution. Neutron-derived displacement parameters independently reveal a strongly enhanced transverse proton displacement, while phonon calculations identify low-frequency transverse modes with the most negative Grüneisen parameters. Together, these results establish the negative thermal expansion of ice I as a collective quantum effect governed by nuclear statistics and the dynamics of the hydrogen-bond network.
