Structural relaxation and stability of a Bi18-cluster as obtained from association of [Bi6O4(OH)(4)](NO3)(6) precursor clusters in DMSO solution is investigated from a combination of quantum chemical calculations and mu s-scale molecular dynamics simulations using empirical interaction potentials. The Bi18-cluster undergoes a OH center dot center dot center dot OH proton transfer reaction, followed by considerable structural relaxation. While the aggregation of the Bi18-cluster is induced by the dissociation of a single nitrate ion leading to [Bi6O4(OH)(4)](NO3)(5)(+) as an activated precursor species that can bind two more Bi6-clusters, we find the [Bi18O13(OH)(10)](NO3)(18+x)(+x) species (explored for x = 1-6) rather inert against either nitrate dissociation, collision with Bi6-precursors or combinations thereof. (C) 2017 Elsevier B.V. All rights reserved.