ABSTRACT
We could not deny most works on ab initio device design are still based on the density functional theory (DFT) [1,2] within the local density approximation (LDA) [1,2]. Actually, this approach has demonstrated good applicability for describing the material structure so far. However, the conventional DFT scheme cannot describe excited states in principle except for the highest occupied state and it is well known that the DFT-LDA calculation yields too smaller band gap than the experiments. Then the practical but ab initio approach that can describe the excited state is highly desired especially for optical device design technology.
