The charge induced by an external electric field is calculated for the Al(001) surface, incorporating the real atomic structure for the first time in such a study. The calculation uses the embedding technique for including the substrate, and the LAPW method to solve the Schrödinger equation in the surface region. The screening charge lies on top of the surface atoms, and its centre of gravity, corresponding to the image plane, lies 1.1 au on the vacuum side of the geometrical surface. With an applied field of +0.01 au (5.14×10 9 V m -1) the Al(001) Shockley surface state is shifted up in energy by +0.001 au (27 meV).