On Apr 11, 2009, at 13:26 , ali kazempoor wrote: > I want to study O vacancy in TiO2 bulk it's tricky, very tricky. May I suggest the following recent paper by Alex Zunger: Phys. Rev. B78, 235104 (2008)? it is a general paper on the problem of formation energies in charged defects. Paolo --- Paolo Giannozzi, Democritos and University of Udine, Italy