Exploratory ab initio and density functional theory calculations are used to locate low-energy minima on the potential energy surface of the formic acid dodecamer (HCOOH)(12). The lowest-energy structures are folded rings, some with a crown-like structure, stabilized by pi-pi interactions. There are many more C-H center dot center dot center dot O interactions than in smaller oligomers. Unlike in tetramers and pentamers, ring structures with one or more monomers in the E (cis) conformation are not significant for dodecamers. (C) 2007 Elsevier B.V. All rights reserved.