Geometric and electronic structures of PdnCum (m + n less than or equal to 6) clusters have been investigated by DFT calculations. Pd4-6 and PdnCum clusters with n greater than or equal to 2 and m + n greater than or equal to 4 are spatial whereas Pd1Cum and Cu-m clusters favor planar shapes. Excess of electron density is shifted towards Pd atom in Pd-Cu bonds and, in spatial particles, towards less coordinated atoms. Bimetallic clusters are usually more stable than monometallic particles of the same size. Stability of bimetallic clusters of the same shape and composition increases linearly with increasing number of Pd-Cu bonds. Pd atoms mix with Cu at every composition, while Cu atoms prefer to segregate at high Cu content. (C) 2004 Elsevier B.V. All rights reserved.