Ab-initio LDA calculations of the mean Coulomb potential V₀ in slabs of crystalline Si, Ge and MgO

The Full Potential Linearized Augmented Plane-Wave (FLAPW) method has been used in the LDA to calculate values of the mean inner Coulomb potential V₀ for Si, Ge and MgO. These values are compared with recent measurements by electron holography. The supercell calculations are performed for crystal slabs, so that the effects of different crystal orientations and surface structures on V₀ can be evaluated. The extent of the fringing potential outside a thin crystal (important for chemical reactions) is also estimated, and this is shown to influence the reference wave in holography experiments. The case of polar crystals and ferroelectrics is discussed briefly. The values published here are needed for electron diffraction studies of bonding and for work aimed at mapping internal fields in semiconductors by electron holography.