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1. Role of sesquiterpenes in biogenic new particle formation

   https://doi.org/10.1126/sciadv.adi5297  

   Dada, Lubna; Stolzenburg, Dominik; Simon, Mario; Fischer, Lukas; Heinritzi, Martin; Wang, Mingyi; Xiao, Mao; Vogel, Alexander L.; Ahonen, Lauri; Amorim, Antonio; et al (September 2023, Science Advances)

   Biogenic vapors form new particles in the atmosphere, affecting global climate. The contributions of monoterpenes and isoprene to new particle formation (NPF) have been extensively studied. However, sesquiterpenes have received little attention despite a potentially important role due to their high molecular weight. Via chamber experiments performed under atmospheric conditions, we report biogenic NPF resulting from the oxidation of pure mixtures of β-caryophyllene, α-pinene, and isoprene, which produces oxygenated compounds over a wide range of volatilities. We find that a class of vapors termed ultralow-volatility organic compounds (ULVOCs) are highly efficient nucleators and quantitatively determine NPF efficiency. When compared with a mixture of isoprene and monoterpene alone, adding only 2% sesquiterpene increases the ULVOC yield and doubles the formation rate. Thus, sesquiterpene emissions need to be included in assessments of global aerosol concentrations in pristine climates where biogenic NPF is expected to be a major source of cloud condensation nuclei. 

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2. Role of base strength, cluster structure and charge in sulfuric-acid-driven particle formation

   https://doi.org/10.5194/acp-19-9753-2019  

   Myllys, Nanna; Kubečka, Jakub; Besel, Vitus; Alfaouri, Dina; Olenius, Tinja; Smith, James Norman; Passananti, Monica (January 2019, Atmospheric Chemistry and Physics)

   Abstract. In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and we systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can also stabilize small clusters for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement. 

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3. Molecular understanding of new-particle formation from <i>α</i>-pinene between −50 and +25 °C

   https://doi.org/10.5194/acp-20-9183-2020  

   Simon, Mario; Dada, Lubna; Heinritzi, Martin; Scholz, Wiebke; Stolzenburg, Dominik; Fischer, Lukas; Wagner, Andrea C.; Kürten, Andreas; Rörup, Birte; He, Xu-Cheng; et al (January 2020, Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. Highly oxygenated organic molecules (HOMs) contributesubstantially to the formation and growth of atmospheric aerosol particles,which affect air quality, human health and Earth's climate. HOMs are formedby rapid, gas-phase autoxidation of volatile organic compounds (VOCs) suchas α-pinene, the most abundant monoterpene in the atmosphere. Due totheir abundance and low volatility, HOMs can play an important role innew-particle formation (NPF) and the early growth of atmospheric aerosols,even without any further assistance of other low-volatility compounds suchas sulfuric acid. Both the autoxidation reaction forming HOMs and theirNPF rates are expected to be strongly dependent ontemperature. However, experimental data on both effects are limited.Dedicated experiments were performed at the CLOUD (Cosmics Leaving OUtdoorDroplets) chamber at CERN to address this question. In this study, we showthat a decrease in temperature (from +25 to −50 ∘C) results ina reduced HOM yield and reduced oxidation state of the products, whereas theNPF rates (J1.7 nm) increase substantially.Measurements with two different chemical ionization mass spectrometers(using nitrate and protonated water as reagent ion, respectively) providethe molecular composition of the gaseous oxidation products, and atwo-dimensional volatility basis set (2D VBS) model provides their volatilitydistribution. The HOM yield decreases with temperature from 6.2 % at 25 ∘C to 0.7 % at −50 ∘C. However, there is a strongreduction of the saturation vapor pressure of each oxidation state as thetemperature is reduced. Overall, the reduction in volatility withtemperature leads to an increase in the nucleation rates by up to 3orders of magnitude at −50 ∘C compared with 25 ∘C. Inaddition, the enhancement of the nucleation rates by ions decreases withdecreasing temperature, since the neutral molecular clusters have increasedstability against evaporation. The resulting data quantify how the interplaybetween the temperature-dependent oxidation pathways and the associatedvapor pressures affect biogenic NPF at the molecularlevel. Our measurements, therefore, improve our understanding of purebiogenic NPF for a wide range of tropospherictemperatures and precursor concentrations. 

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4. Ab Initio Approaches to Simulate Molecular Polaritons and Quantum Dynamics

   https://doi.org/10.1111/wcms.70039  

   Weight, Braden M; Huo, Pengfei (July 2025, WIREs Computational Molecular Science)

   ABSTRACT Molecular polaritons are hybrid states formed by the quantum mechanical interaction between light and matter. Recent experiments have shown the ability to drastically modify chemical reactions in both the ground and excited states through the hybridization of the electronic and photonic degrees of freedom. Ab initio simulations of molecular polaritons have demonstrated similar effects for simple ground and excited state reactions. However, the theoretical community has been limited in its ability to describe the complicated dynamical processes of many‐molecule collective effects with a high‐level treatment of all degrees of freedom within a rigorous Hamiltonian. In this review, we provide a general description and overall procedure for exploring molecular polaritons, leveraging standard many‐body electronic structure calculations combined with the exact, non‐relativistic quantum electrodynamics light‐matter Hamiltonian. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsSoftware > Quantum ChemistryStructure and Mechanism > Reaction Mechanisms and Catalysis 

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5. Fragme∩t : An Open‐Source Framework for Multiscale Quantum Chemistry Based on Fragmentation

   https://doi.org/10.1002/wcms.70058  

   Broderick, Dustin R; Bowling, Paige E; Brandt, Chance; Childress, Sigrún; Shockey, Joshua; Higley, Jonah; Dickerson, Haden; Ahmed, Syed Sharique; Herbert, John M (December 2025, WIREs Computational Molecular Science)

   ABSTRACT Fragment‐based quantum chemistry offers a means to circumvent the nonlinear computational scaling of conventional electronic structure calculations, by partitioning a large calculation into smaller subsystems then considering the many‐body interactions between them. Variants of this approach have been used to parameterize classical force fields and machine learning potentials, applications that benefit from interoperability between quantum chemistry codes. However, there is a dearth of software that provides interoperability yet is purpose‐built to handle the combinatorial complexity of fragment‐based calculations. To fill this void we introduce “Fragme∩t”, an open‐source software application that provides a tool for community validation of fragment‐based methods, a platform for developing new approximations, and a framework for analyzing many‐body interactions.Fragme∩tincludes algorithms for automatic fragment generation and structure modification, and for distance‐ and energy‐based screening of the requisite subsystems. Checkpointing, database management, and parallelization are handled internally and results are archived in a portable database. Interfaces to various quantum chemistry engines are easy to write and exist already for Q‐Chem, PySCF, xTB, Orca, CP2K, MRCC, Psi4, NWChem, GAMESS, and MOPAC. Applications reported here demonstrate parallel efficiencies around 96% on more than 1000 processors but also showcase that the code can handle large‐scale protein fragmentation using only workstation hardware, all with a codebase that is designed to be usable by non‐experts.Fragme∩tconforms to modern software engineering best practices and is built upon well established technologies including Python, SQLite, and Ray. The source code is available under the Apache 2.0 license. This article is categorized under:Electronic Structure Theory > Ab Initio Electronic Structure MethodsTheoretical and Physical Chemistry > ThermochemistrySoftware > Quantum Chemistry 

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