title: Effect of Conformers on Free Energies of Atmospheric Complexes.
abstract: In this article we show how to calculate free energies for atmospherically relevant complexes when multiple conformers and/or isomers are present. We explain why the thermal averaging methods used in several published works are incorrect. On the basis of our two sample cases, the sulfuric acid-pinic acid complex and the (H2SO4)3(NH3)3(H2O)4cluster, we provide numerical evidence that the use of these incorrect formulas can result in errors larger than 1 kcal/mol. We recommend that if vibrational frequencies and thus Gibbs free energies of the individual conformers are unavailable, one should not attempt to correct for the presence of multiple conformers and instead use only the global minimum conformers for both reactants and products. On the contrary, if the free energies for the conformers are calculated for both reactants and products, their effect can be accounted for by the statistical mechanical methods presented in this article.
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry, University of Helsinki , P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014 University of Helsinki, Finland.
authors.forename: Lauri
authors.initials: L
authors.lastname: Partanen
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64 (Gustaff Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Vehkamäki
authors.affiliation: Tianjin International Center of Nanoparticles and Nanosystems, Tianjin University , 92 Weijin Road, Nankai district, Tianjin 300072, P. R. China.|Department of Physics, University of Gothenburg , 41296 Gothenburg, Sweden.
authors.forename: Klavs
authors.initials: K
authors.lastname: Hansen
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64 (Gustaff Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland.
authors.forename: Jonas
authors.initials: J
authors.lastname: Elm
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64 (Gustaff Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland.
authors.forename: Henning
authors.initials: H
authors.lastname: Henschel
authors.affiliation: Laboratory of Physical Chemistry, Department of Chemistry, University of Helsinki , P.O. Box 55 (A.I. Virtasen aukio 1), FIN-00014 University of Helsinki, Finland.
authors.forename: Theo
authors.initials: T
authors.lastname: Kurtén
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64 (Gustaff Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland.
authors.forename: Roope
authors.initials: R
authors.lastname: Halonen
authors.affiliation: Department of Physics, University of Helsinki , P.O. Box 64 (Gustaff Hällströmin katu 2a), FIN-00014 University of Helsinki, Finland.
authors.forename: Evgeni
authors.initials: E
authors.lastname: Zapadinsky