Molecular aggregation effects on the static and dynamic electronic polarizability and hyperpolarizability are estimated within the time-dependent Hartree-Fock scheme by using a decomposition procedure over the atomic orbitals. For each molecule, the total property value consists in an algebraic sum of two contributions: an intrinsic part coming only from the atomic orbitals belonging to the molecule and a mixed contribution coming from the crossed terms associated with atomic orbitals describing the target molecule and its neighbors. All-trans hexatriene molecular clusters are examined to illustrate this decomposition scheme and to analyze the electronic cooperative behavior of the building units. (C) 2003 Elsevier Science B.V. All rights reserved.