title: Does the most stable formic acid tetramer have pi stacking or C-H...O interactions?
abstract: Density functional theory (DFT), Moller-Plesset (MP) perturbation theory, and coupled-cluster calculations are used to examine low-energy minima on the potential energy surface of the formic acid tetramer (HCOOH)(4). The potential energy surface is rather flat with respect to rotation of one of the dimers, relative to the other dimer in an aligned stack, about the axis passing through the inversion centers of the dimers. Our best calculations suggest that an aligned pi-pi stack of two dimers is very likely to be the global minimum but there are two other pi-pi stacks within 0.5 kcal /mol. Moreover, a fourth pi-pi stack, a planar association of two dimers held together by C-H...O interactions, and a bowl structure all lie within 1 kcal /mol of the lowest-energy structure.
authors.affiliation: Institute for Theoretical Chemistry, University of Vienna, Währinger Strasse 17, A-1090 Vienna, Austria. alfred.karpfen@univie.ac.at
authors.forename: Alfred
authors.initials: A
authors.lastname: Karpfen
authors.forename: Ajit J
authors.initials: AJ
authors.lastname: Thakkar
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D003198:Computer Simulation; D019281:Dimerization; D005561:Formates / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008962:Models, Theoretical; D008968:Molecular Conformation; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D011522:Protons; D012680:Sensitivity and Specificity; D012984:Software; D013816:Thermodynamics
chemical_list: D005561:Formates; D011522:Protons; C030544:formic acid; D002244:Carbon; D006859:Hydrogen; D010100:Oxygen