The BeHen+ clusters with n = 1-12 were investigated by ab initio calculations at the level of MP2(full)/6-311+G(2d, 2p). All the most stable geometric structures were obtained. It is found that the first solvation shell around the beryllium ion core is completed at n = 12, and the mechanism of cluster forming can be explained in terms of the solvated ion core model. The effects of basis set superposition error (BSSE) correction and zero-point vibrational energy (ZPE) correction to the energies were considered in the calculations. (C) 2004 Elsevier B.V. All rights reserved.