I型BaAlGe包合物的NMR实验和电子结构计算
NMR experiments and electronic structure calculations in type-I BaAlGe clathrates
摘要：
我们描述了27 Al NMR实验Ba 8AlxGe 46-x I型包合物耦合从头计算研究。对于x=16，从头计算结果确定的计算光谱与测量结果吻合良好，最佳拟合配置也对应于计算的最低能量原子排列。对NMR结果的分析表明，奈特位移的分布在谱线的中心部分占主导地位。计算结果表明，这是由于载流子密度在不同位置上的变化很大。Al缺乏样品与x=12和13表现出分裂的中心NMR峰，信号两个主要的本地环境的Al离子，我们连接到空位的存在。模拟的宽线光谱为x=12表示配置更多的铝在24 k网站比x=16。结果表明，在电子结构中靠近空位的非键杂化物在EF附近的重要性。我们还解决了这些结构中的Pm-3 n对称性的静态失真。
英文摘要：
We describe 27Al NMR experiments on Ba8AlxGe46-x type-I clathrates coupled with ab initio computational studies. For x=16, calculated spectra determined by the ab initio results gave good agreement with the measurements, with best-fitting configurations also corresponding to the computed lowest-energy atomic arrangements. Analysis of the NMR results showed that a distribution of Knight shifts dominates the central portion of the line. Computational results demonstrate that this stems from the large variation of carrier density on different sites. Al-deficient samples with x=12 and 13 exhibited a split central NMR peak, signaling two main local environments for Al ions, which we connected to the presence of vacancies. Modeling of the wide-line spectrum for x=12 indicates a configuration with more Al on the 24k site than for x=16. The results indicate the importance of nonbonding hybrids adjacent to the vacancies in the electronic structure near EF. We also address the static distortions from Pm-3n symmetry in these structures.
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