Cs intercalation has demonstrated experimentally a significant reduction of the work function of carbon nanotubes, thus improving field emission properties. In this paper, we report a density functional theory (DFT) study within the generalized gradient approximation (GGA), regarding the effects of Cs on field emission of single-wall carbon nanotubes (SWCNTs). Specifically, a comprehensive examination was carried out to investigate the effects of Cs adsorbed on capped and open-ended C(5,5) armchair SWCNT tips. Our calculations showed a reduction in the ionization potential (IP) upon Cs physisorption, thus improving the emission properties of carbon nanotubes, as reported experimentally. The structure of the adsorbed Cs-cluster, the corresponding adsorption energies, and the IPs, were altered upon the inclusion of a local electric field in the calculations to mimic the emission environment. (c) 2004 Elsevier B.V. All rights reserved.