发表机构
Rutgers University（罗格斯大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文通过第一性原理晶格动力学结合拉曼光谱与衍射，确定六方金刚石键不对称性为正，澄清其结构争议，指出1529厘米⁻¹特征无法归属于理想2H金刚石。
AI 中文摘要
体相六方金刚石已通过不同路线合成，但其结构仍存在争议：两项最新精修结果甚至对其两种不等价键长差值的符号都未达成一致，差值为238毫埃，且两者均与2003年的早期精修结果存在差异。本文采用第一性原理晶格动力学对这些竞争结构进行检验。在两种泛函下，弛豫后的六方金刚石层间键均比层内键长24毫埃，这是其重叠构象的效应，且该效应与多型体的六方性成正比。亮区中心的$A_{1g}$模式以约-2100厘米⁻¹·埃⁻¹的速率表征层间键，且两种精修坐标均无法复现测量模式的完整图谱。匹配孪晶样品三条谱带的唯一结构需要数十吉帕的围压，且其晶格常数被自身衍射结果排除。拉曼光谱与衍射共同确定了较小的正键不对称性：反相纯样品的光谱推导得$O_B-O_A=24±3$毫埃（95%置信区间），两个独立样品的测定结果分别为+33±8毫埃和+60±45毫埃。1529厘米⁻¹的特征无法归属于均匀理想2H金刚石，而局部高分辨透射电子显微镜（HRTEM）观测仍是一个未解决的难题。
英文摘要
Bulk hexagonal diamond has been synthesized by independent routes, but its structure remains contested: the two recent refinements disagree even on the sign of the difference between its two inequivalent bond lengths, 238~mÅ apart, and both depart from an earlier 2003 refinement. Here we test the competing structures with first-principles lattice dynamics. Relaxed hexagonal diamond has an interlayer bond \emph{longer} than the intralayer bonds by 24~mÅ in both functionals, an effect of its eclipsed conformation that scales with polytype hexagonality. The bright zone-center $A_{1g}$ mode gauges the interlayer bond at $\approx\!-2{,}100$~\icm~Å$^{-1}$, and neither refined coordinate reproduces the full pattern of measured modes. The only structure matching the twinned sample's three bands requires tens-of-gigapascals confining stress and lattice constants excluded by its own diffraction. Raman spectroscopy and diffraction jointly select a small positive bond asymmetry: inverting the spectrum of the phase-pure sample gives $\OB-\OA=24\pm3$~mÅ (95\% interval), and two determinations on separate samples give $+33\pm8$ and $+60\pm45$~mÅ. The 1{,}529~\icm{} feature cannot be assigned to homogeneous ideal 2H diamond, and the local HRTEM observation remains an open puzzle.
