期刊
PHYSICAL REVIEW B
卷 78, 期 19, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.78.195423
关键词
Bethe-Salpeter equation; density functional theory; electron-hole recombination; elemental semiconductors; energy gap; excitons; infrared spectra; nanostructured materials; optical constants; quasiparticles; silicon; ultraviolet spectra; visible spectra
资金
- Austrian FWF [SFB25 IR-ON]
- European Community in the framework of the Network of Excellence NANOQUANTA [NMP4-CT-2004-500198]
- Federal Ministry of Education and Research of Germany [03SF0308]
- NIC Julich [HJN21]
Two state-of-the-art approaches based on the quasiparticle-Bethe-Salpeter equation (QP-BSE) and time-dependent density-functional theory (TDDFT) for different functionals are applied to calculate optical-absorption spectra of Si nanocrystallites passivated with hydrogen. All-electron wave functions are generated within the projector-augmented wave method. The results of the two many-body approaches are used to discuss the interplay of quasiparticle, local-field (LF), and excitonic effects. The QP approach gives rise to blueshifts of the absorption spectra, whereas the LF effects and electron-hole exchange redistribute the oscillator strengths toward higher energies. The screened electron-hole attraction leads to slightly larger optical gaps than the ones found for independent particles described within the local-density approximation (LDA) for exchange and correlation (XC). The results within the TDDFT using the LDA kernel confirm the influence of LF effects. When a hybrid functional for XC is used, the TDDFT spectra show the same tendencies as the QP-BSE ones but still indicate a reduced electron-hole attraction. An effective-medium theory is used to examine the role of local fields due to the nanocrystal arrangement.
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