We describe the building blocks of an effective model employing localized basis functions and non-periodic boundary conditions for the treatment of solvent effects by ab initio molecular dynamics. After sketching the construction of a well sound hybrid potential in a first-principle dynamical framework, we validate the model for a diluted aqueous solution of chloride ion with special reference to the behaviour of different properties with the number of explicit water molecules. The reliability of the results and their stability well below 100 water molecules point out the interest of this new tool in the study of solvent effects. (c) 2006 Elsevier B.V. All rights reserved.