So far, we have been looking at perfect single crystals. At most, we squeezed or deformed them, but even then the regular pattern of atoms kept repeating in the same way up to infinity. However, real crystals as we find them in nature or in the lab, are not always perfect. They contain defects (point defects, line defects, planar defects). Sometimes these defects are innocent, sometimes they contribute in an essential way to the observable properties of the crystal.
How do we model defects by DFT, using codes that have periodic boundary conditions? That’s what this chapter is about. The same strategy — using supercells — can also be used to model surfaces. And also to mimick free atoms. Going thoroughly through this chapter will take you about 2h30m.
Don’t forget the next chapter, which is part of this week’s material too.