Optical spectra of Si nanocrystallites: Bethe-Salpeter approach versus time-dependent density-functional theory

Author(s)

Luis E. Ramos, Joachim Paier, Georg Kresse, F Bechstedt

Abstract

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.

Organisation(s)

Computational Materials Physics

External organisation(s)

Friedrich-Schiller-Universität Jena, Center for Computational Materials Science, CMS

Journal

Physical Review B

Volume

78

No. of pages

9

ISSN

1098-0121

DOI

https://doi.org/10.1103/PhysRevB.78.195423

Publication date

2008

Peer reviewed

Yes

Austrian Fields of Science 2012

103015 Condensed matter

Portal url

https://ucrisportal.univie.ac.at/en/publications/optical-spectra-of-si-nanocrystallites-bethesalpeter-approach-versus-timedependent-densityfunctional-theory(98df5121-97cd-4cfe-808e-1b748b033418).html