胶体核壳量子点中的重应变条件及其对\emph{Ab initio}计算的振动性质的影响
Heavy strain conditions in colloidal core-shell quantum dots and their consequences on the vibrational properties from \emph{Ab initio} calculations
摘要：
我们采用大规模\emph{ab initio}密度泛函理论计算方法研究了具有上千个原子的胶体半导体核壳纳米团簇（半径达15.6 μ m）的晶格应变和振动性质。对于所研究的所有IV族、III-V族和II-VI族半导体，我们发现壳原子的原子位置似乎不受芯材料的影响。特别地，对于IV族核-壳簇，壳材料保持未应变，而核适应于大的晶格失配（压缩或拉伸应变）。对于InAs-InP和CdSe-CdS，核和壳都是压缩应变的，对应于高达20 GPa的压力。我们表明，这种压缩，这有助于一个大的蓝移的振动频率，是抵消，在一定程度上，由近表面壳，这有助于红移的振动模式的欠协调效应。这些发现导致最近的拉曼实验的频移的不同的解释，而他们证实了推测的界面性质的低频肩的高频拉曼峰。
英文摘要：
We preform large-scale \emph{ab initio} density functional theory calculations to study the lattice strain and the vibrational properties of colloidal semiconductor core-shell nanoclusters with up to one thousand atoms (radii up to 15.6~Å). For all the group IV, III-V and II-VI semiconductors studied, we find that the atom positions of the shell atoms, seem unaffected by the core material. In particular, for group IV core-shell clusters the shell material remains unstrained, while the core adapts to the large lattice mismatch (compressive or tensile strain). For InAs-InP and CdSe-CdS, both the cores and the shells are compressively strained corresponding to pressures up to 20 GPa. We show that this compression, which contributes a large blue-shift of the vibrational frequencies, is counterbalanced, to some degree, by the undercoordination effect of the near-surface shell, which contributes a red-shift to the vibrational modes. These findings lead to a different interpretation of the frequency shifts of recent Raman experiments, while they confirm the speculated interface nature of the low-frequency shoulder of the high frequency Raman peak.
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