Effect of inhomogeneity of spin density distribution on the o-p H-2 conversion is investigated by considering the interaction between H-2 and multiple-decked sandwich clusters of M(C6H6)(2) (M= Mn, Fe, Co). We find that the conversion yield for H-2 on Mn(C6H)(2) cluster is greater than those for H-2 on Fe(C6H6)(2) and CO(C6H6)(2) clusters. From the calculation results of spin density distribution of these systems, we find that although the local magnetic moment of Fe in the Fe(C6H6)(2) cluster is the largest compared to Mn in the Mn(C6H)(2) and Co in the CO(C6H6)(2) Clusters, the inhomogeneity of spin density distribution of H-2-Fe(C6H6)(2) cluster is lower than that of the H-2-Mn(C6H6)(2) cluster. Inhomogeneity of spin density distribution thus can be considered as an important factor to look for the best catalyst for the o-p H-2 conversion. (c) 2005 Elsevier B.V. All rights reserved.