Motivated by the experimental demonstration of the actuator action of single-walled carbon nanotubes and in situ resonance Raman experiments, we have performed ab initio restricted Hatree-Fock calculations of the electronic structure of a (5,5) single-walled nanotube in the presence of various ions. We show that the presence of ions near the nanotube causes combined axial and radial deformations of the nanotube. The presence of ions causes a small charge transfer from the ions to the nanotubes as well as changes the pi-pi overlap energy (gamma). We find that the strains developed are primarily due to the electrostatic interactions with only a small contribution from the charge transfer. (c) 2005 Elsevier B.V. All rights reserved.