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Hybrid exchange-correlation functional for accurate prediction of the electronic anD structural properties of ferroelectric oxides. / D. I. Bilc; R. Orlando; R. Shaltaf; G. M. Rignanese; J. Íñiguez; Ph. Ghosez. -In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. -ISSN 1098-ISSN -0121. -77:16(2008, pp. 165107-1-165107-13. Original Citation:Hybrid exchange-correlation functional for accurate prediction of the electronic anD structural properties of ferroelectric oxides. Published version:DOI:10.1103/PhysRevB.77.165107 Terms of use:Open Access (Article begins on next page) Anyone can freely access the full text of works made available as "Open Access". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. Using a linear combination of atomic orbitals approach, we report a systematic comparison of various density functional theory ͑DFT͒ and hybrid exchange-correlation functionals for the prediction of the electronic and structural properties of prototypical ferroelectric oxides. It is found that none of the available functionals is able to provide, at the same time, accurate electronic and structural properties of the cubic and tetragonal phases of BaTiO 3 and PbTiO 3 . Some, although not all, usual DFT functionals predict the structure with acceptable accuracy, but always underestimate the electronic band gaps. Conversely, common hybrid functionals yield an improved description of the band gaps, but overestimate the volume and atomic distortions associated with ferroelectricity, giving rise to an unacceptably large c / a ratio for the tetragonal phases of both compounds. This supertetragonality is found to be induced mainly by the exchange energy corresponding to the generalized gradient approximation ͑GGA͒ and, to a lesser extent, by the exact exchange term of the hybrid functional. We thus propose an alternative functional that mixes exact exchange with the recently proposed GGA of Wu and Cohen ͓Phys. Rev. B 73, 235116 ͑2006͔͒ which, for solids, improves over the treatment of exchange of the most usual GGA's. The new functional renders an accurate description of both the structural and electronic properties of typical ferroelectric oxides. Availability: This is the author's manuscript

We use many-body perturbation theory, the state-of-the-art method for band-gap calculations, to compute the band offsets at the Si/SiO2 interface. We examine the adequacy of the usual approximations in this context. We show that (i) the separate treatment of band structure and potential lineup contributions, the latter being evaluated within density-functional theory, is justified, (ii) most plasmon-pole models lead to inaccuracies in the absolute quasiparticle corrections, (iii) vertex corrections can be neglected, and (iv) eigenenergy self-consistency is adequate. Our theoretical offsets agree with the experimental ones within 0.3 eV.