Energetics of Atmospherically Implicated Clusters Made of Sulfuric Acid, Ammonia, and Dimethyl Amine

Abstract

The formation of atmospheric aerosol particles through clustering of condensable vapors is an important contributor to the overall concentration of these atmospheric particles. However, the details of the nucleation process are not yet well understood and are difficult to probe by experimental means. Computational chemistry is a powerful tool for gaining insights about the nucleation mechanism. Here, we report accurate electronic structure calculations of the potential energies of small clusters made from sulfuric acid, ammonia, and dimethylamine. We also assess and validate the accuracy of less expensive methods that might be used for the calculation of the binding energies of larger clusters for atmospheric modeling. The PW6B95-D3 density-functional-plus-molecular-mechanics calculation with the MG3S basis set stands out as yielding excellent accuracy while still being affordable for very large clusters.

Computational approaches for efficiently modelling of small atmospheric clusters

“…Based on recent benchmarks, we utilize the DFT functionals M06-2X, PW91 and ωB97X-D, which have been identified to perform well in describing clusters of atmospheric relevance [19,20,[24][25][26]. While these three functionals show relatively similar performance they are constructed very differently.…”

Reply to the ‘Comment on “Enhancement in the production of nucleating clusters due to dimethylamine and large uncertainties in the thermochemistry of amine-enhanced nucleation”’ by Kupiainen-Maatta et al.

“…However, this claim is unfounded and misleading. In order to support their claim, KM cited two recent studies from the Helsinki group [15,17]. However, the study [17] is limited, as evidenced by the captions to Tables 1 and 2 in [17], to benchmarking the electronic energy, which is just one of the components of the Gibbs free energy, and, hence, no conclusion about predictions of Gibbs free energy changes could have ever been made in [17].…”

On the stability and dynamics of (sulfuric acid)(ammonia) and (sulfuric acid)(dimethylamine) clusters: A first-principles molecular dynamics investigation

“…All the simulations were performed using the CP2K program package (www.cp2k.org) and the forces were calculated within Kohn-Sham density functional theory as implemented in the Quickstep [25] module of CP2K. We used the PBE functional [27], which has been previously shown to work well for polar hydrogen-bonding liquids [28,29] and recently in the context of atmospheric clusters [30,31]. The density functional was used with a dual basis set method [26]: a doubly polarized triple-f Gaussian-type basis set in real-space and a plane-wave basis set with a cut-off of 600 Ry in the momentum-space.…”