Abstract
Using density-functional theory with the local density approximation for exchange and correlation the authors calculated self-consistently the response of the electrons at the surface of a semi-infinite jellium for strong external fields. The linear and non-linear contributions to the response were separated. The response is characterised by the centre of the induced charge density and the width of its first extremum. The variation of the centre of the induced charge density with the external field is compared with results from simple Smith model density calculations, in which different approaches for obtaining the variational parameter are used.