The ground state of the neutral atoms Rb through Xe and their corresponding cations has been studied by using explicitly correlated wave functions in a non relativistic approach. The variational wave function has been previously used to study the neutral atoms Li through Kr and their cations. The ionization potential of these atoms has been calculated by including relativistic effects perturbatively. The calculation has been carried out by using the variational Monte Carlo method. (C) 2008 Elsevier B.V. All rights reserved.