159 research outputs found
Calculated two-photon electronic transitions in sulfuric acid and its atmospheric relevance
Non Peer reviewe
Hydration of Atmospheric Molecular Clusters III : Procedure for Efficient Free Energy Surface Exploration of Large Hydrated Clusters
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.Peer reviewe
Subphthalocyanine-triangulene dyads: Property tuning for light-harvesting device applications
Organic photovoltaics relies on the development of stable chromophores and redox-active organic molecules with tailor-made HOMO/LUMO energies. Here, we present the synthesis and properties of novel dyads composed of boron subphthalocyanine (SubPc) and triangulene units, connected either at the peripheral position of the subphthalocyanine or at the axial boron. The connectivity has strong implications for the absorption and fluorescence properties of the dyads, as well as their redox properties. While the SubPc unit has a bowl shape, triangulene is a planar structural unit that allows dyads to dimerize in the solid state on account of π-stacking interactions as shown by X-ray crystallography of one of the dyads. The electronic properties were also studied computationally by density functional theory methods. Excellent agreement between experimental and computed data were obtained, showing that our computational method is a strong tool in the rational design of optimum molecules to ultimately obtain finely tuned molecules for device applications.
Keywords: chromophores; conjugation; molecular engineering; redox‐active molecules; structure–property relationship
Hydration of Atmospheric Molecular Clusters II: Organic Acid-Water Clusters
Using
computational methods, we study the gas phase hydration of
three different atmospherically relevant organic acids with up to
10 water molecules. We study a dicarboxylic acid (pinic acid) and
a tricarboxylic acid (3-methyl-1,2,3-butanetricarboxylic acid (mbtca))
that are both identified as products from α-pinene oxidation
reactions. We also study a 2-oxohexanediperoxy acid (ohdpa) that has
been identified as a product from cyclohexene autoxidation. To sample
the cluster structures, we employ our recently developed systematic
hydrate sampling technique and identify a total of 551 hydrate clusters.
The cluster structures and thermochemical parameters (at 298.15 K
and 1 atm) are obtained at the ωB97X-D/6-31++G(d,p) level of
theory, and the single point energy of the clusters have been refined
using a high level DLPNO–CCSD(T)/aug-cc-pVTZ calculation. We
find that all three tested organic acids interact significantly more
weakly with water compared to the primary nucleation precursor sulfuric
acid. Even at 100% relative humidity (298.15 K and 1 atm), we find
that ohdpa remains unhydrated and only the monohydrate of pinic acid
and mbtca are slightly populated (4% and 2%, respectively). From the
obtained molecular structures, potential implications for the ice
nucleating ability of aerosol particles is discussed
Searching the Chemical Space of Bicyclic Dienes for Molecular Solar Thermal Energy Storage Candidates
Photoswitches are molecular systems that are chemically transformed subsequent to interaction with light and they find potential application in many new technologies. The design and discovery of photoswitch candidates require intricate molecular engineering of a range of properties to optimize a candidate to a specific applications, a task which can be tackled efficiently using quantum chemical screening procedures. In this paper, we perform a large scale screening of approximately half a million bicyclic diene photoswitches in the context of molecular solar thermal energy storage using ab initio quantum chemical methods. We further device an efficient strategy for scoring the systems based on their predicted solar energy conversion efficiency and elucidate potential pitfalls of this approach. Our search through the chemical space of bicyclic dienes reveals systems with unprecedented solar energy conversion efficiencies and storage densities that show promising design guidelines for next generation molecular solar thermal energy storage systems
Photo- and Collision-Induced Isomerization of a Charge-Tagged Norbornadiene–Quadricyclane System
Molecular photoswitches based on the norbornadiene-quadricylane (NBD-QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes. To characterize the intrinsic properties of such systems, reversible isomerization of a charge-tagged NBD-QC carboxylate couple is investigated in a tandem ion mobility mass spectrometer, using light to induce intramolecular [2 + 2] cycloaddition of NBD carboxylate to form the QC carboxylate and driving the back reaction with molecular collisions. The NBD carboxylate photoisomerization action spectrum recorded by monitoring the QC carboxylate photoisomer extends from 290 to 360 nm with a maximum at 315 nm, and in the longer wavelength region resembles the NBD carboxylate absorption spectrum recorded in solution. Key structural and photochemical properties of the NBD-QC carboxylate system, including the gas-phase absorption spectrum and the energy storage capacity, are determined through computational studies using density functional theory
Coupled cluster theory on modern heterogeneous supercomputers
This study examines the computational challenges in elucidating intricate chemical systems, particularly through ab-initio methodologies. This work highlights the Divide-Expand-Consolidate (DEC) approach for coupled cluster (CC) theory—a linear-scaling, massively parallel framework—as a viable solution. Detailed scrutiny of the DEC framework reveals its extensive applicability for large chemical systems, yet it also acknowledges inherent limitations. To mitigate these constraints, the cluster perturbation theory is presented as an effective remedy. Attention is then directed towards the CPS (D-3) model, explicitly derived from a CC singles parent and a doubles auxiliary excitation space, for computing excitation energies. The reviewed new algorithms for the CPS (D-3) method efficiently capitalize on multiple nodes and graphical processing units, expediting heavy tensor contractions. As a result, CPS (D-3) emerges as a scalable, rapid, and precise solution for computing molecular properties in large molecular systems, marking it an efficient contender to conventional CC models
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