Assessment of Density Functional Theory in Predicting Structures and Free Energies of Reaction of Atmospheric Prenucleation Clusters

This work assesses different computational strategies for predicting structures and Gibb's free energies of reaction of atmospheric prenucleation clusters. The performance of 22 Density Functional Theory functionals in predicting equilibrium structures of molecules and water prenucleation clusters of atmospheric relevance is evaluated against experimental data using a test set of eight molecules and prenucleation clusters: SO2, H2SO4, CO2 center dot H2O, CS2 center dot H2O, OCS center dot H2O, SO2 center dot H2O, SO3 center dot H2O, and H2SO4 center dot H2O. Furthermore, the functionals are tested and compared for their ability to predict the free energy of reaction for the formation of five benchmark atmospheric prenucleation clusters: H2SO4 center dot H2O, H2SO4 center dot(H2O)(2), H2SO4 center dot NH3, HSO4 center dot H2O, and HSO4-center dot(H2O)(2). The performance is evaluated against experimental data, coupled cluster, and complete basis set extrapolation procedure methods. Our investigation shows that the utilization of the M06-2X functional with the 6-311++G(3df,3pd) basis set represents an improved approach compared to the conventionally used PW91 functional, yielding mean absolute errors of 0.48 kcal/mol and maximum errors of 0.67 kcal/mol compared to experimental results.