Comment on "Quantum Confinement and Optical Gaps in Si Nanocrystals"
  We show that the method used by Ogut, Chelikowsky and Louie (Phys. Rev. Lett. 79, 1770 (1997)) to calculate the optical gap of Si nanocrystals omits an electron-hole polarization energy. When this contribution is taken into account, the corrected optical gap is in excellent agreement with semi-empirical pseudopotential calculations. 
Alberto Franceschetti, Lin-Wang Wang, and Alex Zunger