In this work, we present non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM) simulations of the (001) surface of silver and supported MgO thin films. From the calculated force spectroscopy, we predict atomic resolution at tip-surface distances of less than 5 A. For KPFM, we study the influence of charges localized on either the tip or on the surface on the Kelvin voltage. It is shown that the Kelvin voltage changes when the tip is placed above an MgO monolayer, only if the layer has a permanent net dipole. For point charges on the silver surface we examine the lateral resolution in the distance range of 1 to 3 nm, which is the standard working distance in KPFM. We show that point charges appear as nanometer large spots in Kelvin images, which is due to a long-range electrostatic interaction with the tip apex. [DOI: 10.1380/ejssnt.2011.6]