Surface effects in Si interstitial formation energies

We are calculating Si self-interstitial formation energies using Density Functional Theory and several different exchange-correlation energy functionals. We show that the difference in results obtained with the LDA, PBE, PW91, and AM05 [1] functionals can be explained by the functionals' different surface intrinsic errors. We explain why surface effects are important for formation energies of interstitials in semi-conductors. Surface effects have previously been studied for metal vacancy formation energies. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [1] R. Armiento and A. E. Mattsson, Phys. Rev. B {\bf 72}, 085108 (2005).