First-principles calculations have been performed to study the electronic band structure and its magnetic property for the compound of bis(ethylenediselena)-tetrathiafulvalene(BEST) with the paramagnetic hexacyanoferrate(III) [Fe(CN)(6)](3-) or the photochromic nitroprusside anion [Fe(CN)(5)NO](2-). From the total and partial density of states and atomic spin magnetic moments, it is found that the spin magnetic moments of (BEST)(4)[Fe(CN)(6)] is mainly assembled at the iron atom and the cyanogen radical and the spontaneous magnetic moments for (BEST)(2)[Fe(CN)(5)NO] come from iron atom, cyanogen and nitric oxide radical. In particular, there exist small magnetic moments at Se and S atoms and there formed the alternating +/-/+ spin population of C/Se/S, which means there exists antiferromagnetic exchange interaction in the organic layers. (C) 2003 Elsevier B.V. All rights reserved.