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 (HSO)(NH)(HO) cluster, 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.

Propionamide participating in H2SO4-based new particle formation: a theory study

“…In the case, when ABCluster was used, 1000 automatically generated structures were optimized using the semi-empirical PM6 method. 29,30 Then, up to 100 low-energy structures were selected to rene at the B3LYP/6-31g(d,p) level of theory to get 30 lowest energy isomers. At the nal stage, these 30 lowest energy isomers were optimized at the M06-2X/6-311++G(3df, 3pd) level of theory.…”

What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?

“…[79][80][81]83 The pinic acid and MBTCA cluster structures have been taken from previous studies. 59,84 It should be noted that we use the monomer of pinic acid as identified in reference, 85 as it is 1.0 kcal/mol more stable than the identified global minimum energy conformer in our original paper. 59 The 3hydroxy-glutaric acid, terebic acid and terpenylic acid cluster structures have been identified using the same semi-empirically guided sampling technique as outlined in section 2.1.…”

Rigorous Conformational Analysis of Pyrrolidine Enamines with Relevance to Organocatalysis

“…For details on the protocol applied, the uncertainty associated with these approximations, and how to account for conformational flexibility, see the and Refs. . Considering the conformational flexibility of reactants is clearly important and we may refer to Refs.…”