Theoretical methods based on density functional theory have been employed to analyze the exchange interactions in an Fe 10 complex. The calculated exchange coupling constants are in excellent agreement with those obtained previously by fitting the experimental data using classic Monte-Carlo simulations. The relative stabilities of the spin states obtained by a diagonalization of the matrix Hamiltonian using the Lanczos algorithm have been studied. These results show that the S value of the ground state is extremely sensitive to the J values, thus, a very small change of the exchange coupling constants could modify the total spin of the molecule. (c) 2005 Elsevier B.V. All rights reserved.