An approach to describe heteroatomic clusters A(n)B(N-n) as perturbed homoatomic ones is presented. By first treating the homoatomic systems A(N) or/and B-N and subsequent application of first-order perturbation theory it is possible to estimate relative stabilities of the 2(N) possible distributions of the atom types A and B at the N atomic sites in a very efficient manner. The approach was tested considering IrnPt13-n as an example (treated with density functional methods). One observes good correlation between relative stabilities estimated from the homoatomic cases and those obtained from explicit treatments of the binary systems. Moreover we rationalize the observed correlation of atom type and atom position in IrnPt13-n. (C) 2004 American Institute of Physics.