The potential energy surface and hyperpolarizabilities of the core (G0) and the first generation (G1) of polyamidoamide (PAMAM) dendrimer are studied by using the density functional theory with both the basis sets optimized for B3LYP method and the medium-size polarized GTO/CGTO basis sets for calculations of molecular polarizability. The inversion barrier of G1 is 941.4 cm(-1), which indicates that the back folding of the branches is very easy for this dendrimer construction. It is found that in most cases, the first hyperpolarizabilities beta of G1 will increased when the molecular structure is distorted from its equilibrium arrangement. These results provide structural guidelines for the optimization of beta by means of changing the dendrimer shape in different solvents. (C) 2002 Elsevier Science B.V. All rights reserved.