#Semiempirical quantum chemical treatment at the level of PM3 type calculations were performed on the models considered to be capable of mimicking [NiFe] hydrogenase core of Desulfovibrio vulgaris Miyazaki F at different mechanistic steps. These models possess H, S or Se bridge between Ni and Fe centers. In the case of neutral models URF, whereas for the charged models RHF type approach were used. In every case, the models were found to be stable and exothermic. The calculations also revealed that Se bridge, up to a first approximation, may take over the role of S bridge, although the existence of such [NiFe] hydrogenase for D. vulgaris has not been reported yet. (C) 2003 Elsevier B.V. All rights reserved.