We discuss the effects of a static long-range contribution -alpha/q(2) to the exchange-correlation kernel f(xc)(q) of time-dependent density functional theory. We show that the optical absorption spectrum of solids exhibiting a strong continuum excitonic effect is considerably improved with respect to calculations where the adiabatic local-density approximation is used. We discuss the limitations of this simple approach, and in particular that the same improvement cannot be found for the whole spectral range including the valence plasmons and bound excitons. On the other hand, we also show that within the range of validity of the method, the parameter alpha depends linearly on the inverse of the dielectric constant, and we demonstrate that this fact can be used to predict continuum excitonic effects in semiconductors. Results are shown for the real and imaginary part of the dielectric function of Si, GaAs, AlAs, diamond, MgO, SiC and Ge, and for the loss function of Si.
|Number of pages||14|
|Journal||Physical Review B|
|Publication status||Published - Apr 2004|
Bibliographical note© 2004 American Physical Society.
- ELECTRON-HOLE EXCITATIONS
- INTERBAND CRITICAL-POINTS
- QUASI-PARTICLE THEORY
- DIELECTRIC FUNCTION