Density functional theoretical studies of the isomers of croconic acid and their dimers

► The two isomers (A and B) of croconic acid and their dimers have been examined by density functional methods. ► Isomer A has a lower (more negative) energy than isomer B. ► The hydrogen bonding between two molecules of B is stronger than that between two molecules of A. ► The formation of dimers by hydrogen bonding from all possible sites has been examined.