1302.6972 (Zeng-hui Yang et al.)

Direct calculation of exciton binding energies with time-dependent
density-functional theory    [PDF]

Zeng-hui Yang, Carsten A. Ullrich

Excitons are electron-hole pairs appearing below the band gap in insulators and semiconductors. They are vital to photovoltaics, but are hard to obtain with time-dependent density-functional theory (TDDFT), since most standard exchange-correlation (xc) functionals lack the proper long-range behavior. Furthermore, optical spectra of bulk solids calculated with TDDFT often lack the required resolution to distinguish discrete, weakly bound excitons from the continuum. We develop a method analogous to the Casida equation formalism for molecular excitations, in which exciton binding energies are obtained directly. We calculate exciton binding energies for both small- and large-gap semiconductors and insulators, study the recently proposed bootstrap xc kernel [S. Sharma {\em et al.}, Phys. Rev. Lett. {\bf 107}, 186401 (2011)], and extend the formalism to triplet excitons.

View original: http://arxiv.org/abs/1302.6972