Structural and Electronic Properties of PbSe Nanocrystals from First Principles
Structural and Electronic Properties of PbSe Nanocrystals from First Principles
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DOI：
10.1103/physrevb.78.075418
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发表时间：
2008-08
影响因子：
3.7
通讯作者：
A. Franceschetti
中科院分区：
文献类型：
--
作者：
A. Franceschetti
本文报道了半径为8.4 ~ 14.8埃的PbSe纳米晶体的结构和电子特性的密度泛函计算。我们考虑了接近球形的岩盐结构纳米晶体，其Pb:Se化学计量比为1:1，表面没有吸附的分子物质。我们发现：(1)在靠近纳米晶体表面的{约}8-{埃}厚的壳层中，与块状PbSe相比，Pb-Se键长和键角明显扭曲。(2)即使在没有表面钝化剂的情况下，纳米晶体的带隙中也不存在表面态。(3)当一个电子从价带提升到导带时，纳米晶体带隙发生了明显的红移（frank - condon shift）。对于半径R=8.4{埃}的纳米晶体，计算得到的frank - condon位移为{约}0.18 eV。(4)计算得到的态电子密度在价态和导态之间存在明显的不对称性，表明价带和导带之间不存在“镜像对称”。
This work reports density-functional calculations of the structural and electronic properties of PbSe nanocrystals ranging in radius from 8.4 to 14.8 {angstrom}. We considered nearly spherical, rocksalt-structure nanocrystals with 1:1 Pb:Se stoichiometry and no molecular species adsorbed at the surface. We found that: (1) The Pb-Se bond lengths and bond angles are significantly distorted compared to those in bulk PbSe, in an {approx} 8-{angstrom}-thick shell near the surface of the nanocrystal. (2) Even in the absence of surface passivants, there are no surface states in the band gap of the nanocrystals. (3) The nanocrystal band gap undergoes a significant redshift (Franck-Condon shift) when an electron is promoted from the valence band to the conduction band. For nanocrystals of radius R=8.4 {angstrom}, the calculated Franck-Condon shift is {approx}0.18 eV. (4) The calculated electronic density of states shows a significant asymmetry between valence and conduction states, suggesting that the postulated 'mirror symmetry' between valence band and conduction band does not exist.