In the present paper, we focus on the diffusion behaviour of cesium atoms implanted into silicon. This aspect has not been investigated directly up to now but is of utmost importance to understand the ionisation mechanisms in more detail. Density functional theory calculations combined with ab initio molecular dynamics simulations have been used to study the different aspects of cesium diffusion to the sample surface as a function of cesium concentration and sample temperature. In general, the solubility of cesium atoms in a silicon matrix is small, and the diffusion of the cesium atoms towards the surface is almost immediate, depending on how and where the cesium atom is incorporated in the silicon lattice. Depending on the defects introduced into the Si substrate, the diffusion could be largely reduced or cannot be observed during the few picosecond time range that can be explored by ab initio molecular dynamics simulations. Copyright © 2014 John Wiley & Sons, Ltd.