We introduce a simple model to predict whether the first water bilayer on hexagonal metal surfaces grows two- or three-dimensionally and compare the predictions of the new model with experimental data. Water-water interaction energies were calculated with the classical interaction potential TIP4P and quantum chemically (RHF, RMP2, RMP4(SDTQ) and B3LYP with the DZP and aug-cc-pVDZ basis sets). The metal surface was replaced by an hexagonal mesh of auxiliary geometrical points (a virtual surface) and additional water-metal interaction energies were approximated with a Morse potential. (C) 2002 Elsevier Science B.V. All rights reserved.