第6族双六配位（η⁶-η⁶）双层石墨烯的费米能级金属d特性
Fermi-Level Metal-d Character of Group-6 Bis-Hexahapto Bilayer Graphene
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中文总结 AI 辅助
该研究探究第6族双六配位双层石墨烯的费米能级特性，发现其费米能级态以金属d为主而非碳p，不具备超导石墨插层化合物的层间带特性。
中文摘要 AI 辅助
石墨插层化合物的超导性需要由电正性插层剂提供的电荷填充碳衍生的层间带。双六配位（η⁶-η⁶）将过渡金属与两层石墨烯共价结合，电荷转移极少——这种化学机制消除了插层石墨超导性所依赖的电荷捐赠。我们针对双层石墨烯中的第6族Cr、Mo和W，探究费米能级态是否保留离子参考体系的间隙碳p特性，并以块体CaC₆及同胞C₁₂Ca/C₁₂Li作为对照。未计算电子-声子耦合。在每个画廊含1个金属（C₁₂M）的情况下，离子对照体系在费米能级（EF）处经原子掩蔽的间隙区域中，分别保留了68%和45%的画廊光谱权重；而第6族体系分别保留15%、22%和23%。这种差异源于组成：第6族画廊的绝对间隙权重比C₁₂Li更多，但在EF附近±0.15 eV范围内的投影态密度，离子对照体系以碳p为主，而三种第6族双层均以金属d为主（约73%）。所有研究体系均为金属；它们的费米表面承载物不同。几何上，η⁶-η⁶配位要求AA堆叠，且在金属存在处将本征伯纳尔（Bernal）偏好反转400-600 meV。有序相对块体金属是亚稳态（每原子+2.9-5.0 eV），但对孤立原子是稳定的（每原子-1.6-4.1 eV）；不稳定性排序（Cr最小，W最大）与Cr > Mo > W的反应性匹配。C₁₂Cr为金属；仅钨携带0.65 μB。双六配位插层提供强层间键合和确定的AA晶格，但不具备与超导石墨插层化合物相关的层间带特性。
英文摘要
Superconductivity in graphite intercalation compounds requires occupancy of a carbon-derived interlayer band filled by charge from an electropositive intercalant. Bis-hexahapto (eta6-eta6) coordination binds transition metals covalently to two graphene sheets with little charge transfer: the mechanism defining this chemistry removes the donation that superconductivity rests on. We ask, for group-6 Cr, Mo and W in bilayer graphene, whether Fermi-level states retain the interstitial, carbon-p character of ionic references, with bulk CaC6 and same-cell C12Ca/C12Li controls. Electron-phonon coupling is not computed. At one metal per gallery (C12M), the ionic controls retain 68 and 45 per cent of gallery spectral weight in atom-masked interstitial regions at EF; the group-6 systems retain 15, 22 and 23 per cent. The contrast is compositional: group-6 galleries carry more absolute interstitial weight than C12Li, but projected density of states within +/-0.15 eV of EF is carbon dominated in the ionic references and metal dominated (~73 per cent, of which 89-98 per cent is d) in all three group-6 bilayers. Every system studied is metallic; they differ in what carries the Fermi surface. Zone-centre phonons are clean for all three ordered bilayers; the pristine AA bilayer is not, its unstable mode being the AA-to-AB shear. Geometrically, eta6-eta6 coordination requires AA stacking and reverses the intrinsic Bernal preference by 400-600 meV wherever metal is present. Ordered phases are metastable against bulk metal (+2.9-5.0 eV per atom) but bound against isolated atoms (-1.6-4.1 eV); instability ordering (Cr least, W most) matches Cr > Mo > W reactivity. C12Cr is metallic; tungsten alone carries 0.65 muB. Bis-hexahapto intercalation delivers strong interlayer bonding and a definite AA registry, but not the interlayer-band character of superconducting graphite intercalation compounds.
