Assessing the Interactions in Atmospherically Relevant Sulfuric Acid‐Carboxylic Acid Clusters

Abstract Clusters of atmospheric precursor molecules, like sulfuric acid, bisulfate, and organic carboxylic acids, are important embryos for the formation of aerosol particles, further impacting both the earth radiation budget, cloud formation, and daily life. In this work, we studied theoretically the structures, energetics, and interactions of a cluster formed between HSO 4 – and acetic acid: HSO 4 – •H + •CH 3 COO – , which stands for the uncertain location of the proton, either on HSO 4 – end or on CH 3 COO – end. We checked the performance of second‐order Møller–Plesset perturbation theory (MP2) and several density functional theory methods, including BP86, PW91, PBE0, B3LYP, M06‐2X, CAM‐B3LYP, ωB97XD, and B2PLYP with both double‐ζ and triple‐ζ basis sets. We found that overall M06‐2X has good performance for the structures and energetics, and is suggested to be the choice for calculating similar kind of aerosol clusters, but B3LYP also has acceptable performance for optimizing the structures, in particular when dispersion corrections are included. We also found that HSO 4 – •H + •CH 3 COO – has two almost energy degenerate hydrogen bonded isomers, that is, HSO 4 – (CH 3 COOH) and H 2 SO 4 (CH 3 COO – ), and energy decomposition analysis revealed that electrostatic interaction dominates the hydrogen bonding interactions for both isomers, followed by exchange and orbital interactions.