Hydration of Atmospheric Molecular Clusters III: Procedure for Efficient Free Energy Surface Exploration of Large Hydrated Clusters

Freja Rydahl Rasmussen, Jakub Kubecka, Vitus Besel, Hanna Vehkamäki, Kurt V. Mikkelsen, Merete Bilde, Jonas Elm

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Sampling the shallow free energy surface of hydrated atmospheric molecular clusters is a significant challenge. Using computational methods, we present an efficient approach to obtain minimum free energy structures for large hydrated clusters of atmospheric relevance. We study clusters consisting of two to four sulfuric acid (sa) molecules and hydrate them with up to five water (w) molecules. The structures of the "dry" clusters are obtained using the ABCluster program to yield a large pool of low-lying conformer minima with respect to free energy. The conformers (up to ten) lowest in free energy are then hydrated using our recently developed systematic hydrate sampling technique. Using this approach, we identify a total of 1145 unique (sa)(2-4)(w)(1-5) cluster structures. The cluster geometries and thermochemical parameters are calculated at the omega B97X-D/6-31++G(d,p) level of theory, at 298.15 K and 1 atm. The single-point energy of the most stable clusters is calculated using a high-level DLPNO-CCSD(T-0)/aug-cc-pVTZ method. Using the thermochemical data, we calculate the equilibrium hydrate distribution of the clusters under atmospheric conditions and find that the larger (sa)(3) and (sa)(4) clusters are significantly more hydrated than the smaller (sa)(2) cluster or the sulfuric acid (sa)(1) molecule. These findings indicate that more than five water molecules might be required to fully saturate the sulfuric acid clusters with water under atmospheric conditions. The presented methodology gives modelers a tool to take the effect of water explicitly into account in atmospheric particle formation models based on quantum chemistry.

Original languageEnglish
JournalJournal of Physical Chemistry A
Volume124
Issue number25
Pages (from-to)5253-5261
Number of pages9
ISSN1089-5639
DOIs
Publication statusPublished - 25 Jun 2020
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 114 Physical sciences
  • AB-INITIO
  • AMINES
  • BINDING-ENERGIES
  • DIMETHYLAMINE
  • NUCLEATION
  • PARTICLE FORMATION
  • STABILITY
  • SULFURIC-ACID DIMERS
  • THERMOCHEMISTRY
  • WATER CLUSTERS

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