The one-dimensional intermolecular ferromagnetic interaction of a charge-transfer (CT) complex, (BDTA)[Ni(mnt)(2)] (BDTA: 1,3,2-benzodithiazolyl, mnt: maleonitriledithiolate), is studied by the Kohn-Sham hybrid density functional method, in order to understand the mechanism of the magnetism. All possible effective exchange integrals, J, between the spin pairs of the system indicate that a ferromagnetic interaction (J = 172 cm(-1)) exists along the b-axis. Magnetic susceptibility, simulated with the ab initio determined J values by the quantum Monte Carlo (QMC) method, is qualitatively consistent with that measured experimentally. (c) 2005 Elsevier B.V. All rights reserved.