  The interaction energy between a water molecule and graphitic structured
clusters terminated by hydrogen atoms is analyzed by ab initio methods and
decomposed into electrostatic, induction, Pauli repulsion, and correlation
energy contributions. Contributions to the energy which are due solely to the
perimeter of the clusters are identified. These can be isolated and discarded
which greatly simplifies the problem of extrapolation to the large cluster
limit. The remaining terms are intrinsic to the interaction of a water molecule
with real graphitic layers and an explicit analytical form is given for the
potential energy surface. The minimum energy configuration is found to have
both hydrogen atoms of the water molecule pointing symmetrically away from the
graphitic plane. The electronic interaction in this mode is -16.8 +/- 1.7
kJ/mol for water-graphite and the zero point energy is estimated as 1.3 kJ/mol.
