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Electronic and optical excitations in Ag_n clusters (n = 1-8):Comparison of density-functional and many-body theories

机译:Ag_n团簇(n = 1-8)中的电子和光激发:密度泛函理论和多体理论的比较

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We analyze the electronic and optical excitations in silver clusters (Ag_n, n=1-8) using density-functional and many-body theories within an ab initio pseudopotential framework. Vertical ionization potentials and electron affinities are calculated within the so-called ΔSCF and GW approximations. Results are compared with experimental datae, For molecular orbitals of predominantly sp character, the GW results are found to be in good agreement with experiment. For orbitals of mainly d character, good agreement with experiment can be achieved only via the use of semicore pseudopotentials, due to strong correlations among 4s, 4p, and 4d electrons. Optical excitations are computed within the time-dependent local-density approximation (TDLDA) and by solving the Bethe-Salpeter equation (BSE) for electrons and holes. For most clusters, the TDLDA spectra are in reasonable agreement with experimental data. The optical excitations computed with the BSE method, on the other hand, are generally in poor agreement with experiment, especially as size increases. This finding is explained in terms of the nonlocality of the BSE kernel and correlations involving Ad electrons. We also discuss the roles played by self-consistency, vertex corrections, and satellite structures in the GW results of these confined systems with d valence electrons.
机译:我们使用从头算伪电位框架内的密度泛函和多体理论分析了银团簇(Ag_n,n = 1-8)中的电子和光学激发。在所谓的ΔSCF和GW近似值内计算垂直电离势和电子亲和力。将结果与实验数据进行比较,发现对于主要为sp特性的分子轨道,GW结果与实验吻合良好。对于主要为d特性的轨道,由于4s,4p和4d电子之间的强相关性,只有通过使用半芯假电位才能与实验取得良好的一致性。在与时间有关的局部密度近似(TDLDA)内,并通过求解电子和空穴的Bethe-Salpeter方程(BSE),计算出光激发。对于大多数星团,TDDLA光谱与实验数据合理吻合。另一方面,用BSE方法计算的光激发通常与实验不一致,尤其是随着尺寸的增加。根据BSE核的非局部性和涉及Ad电子的相关性来解释此发现。我们还将讨论自洽,顶点校正和卫星结构在这些带有d价电子的受限系统的GW结果中所扮演的角色。

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