posted on 2023-11-13, 14:39authored byHaide Wu, Morten Engsvang, Yosef Knattrup, Jakub Kubečka, Jonas Elm
The nucleation process
leading to the formation of new
atmospheric
particles plays a crucial role in aerosol research. Quantum chemical
(QC) calculations can be used to model the early stages of aerosol
formation, where atmospheric vapor molecules interact and form stable
molecular clusters. However, QC calculations heavily depend on the
chosen computational method, and when dealing with large systems,
striking a balance between accuracy and computational cost becomes
essential. We benchmarked the binding energies and structures and
found the B97-3c method to be a good compromise between the accuracy
and computational cost for studying large cluster systems. Further,
we carefully assessed configurational sampling procedures for targeting
large atmospheric molecular clusters containing up to 30 molecules
(approximately 2 nm in diameter) and proposed a funneling approach
with highly improved accuracy. We find that several parallel ABCluster
explorations lead to better guesses for the cluster global energy
minimum structures than one long exploration. This methodology allows
us to bridge computational studies of molecular clusters, which typically
reach only around 1 nm, with experimental studies that often measure
particles larger than 2 nm. By employing this workflow, we searched
for low-energy configurations of large sulfuric acid–ammonia
and sulfuric acid–dimethylamine clusters. We find that the
binding free energies of clusters containing dimethylamine are unequivocally
more stable than those of the ammonia-containing clusters. Our improved
configurational sampling protocol can in the future be applied to
study the growth and dynamics of large clusters of arbitrary compositions.