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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
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Quantum cluster equilibrium model of N-methylformamide-water binary mixtures
Michael von Domaros1, Sascha Jähnigen2, Joachim Friedrich3
1Mulliken Center for Theoretical Chemistry, Universität Bonn, Beringstr. 4, D-53115 Bonn, Germany.
The Journal of Chemical Physics
|February 15, 2016
Summary
Refined quantum cluster equilibrium (QCE) calculations for N-methylformamide (NMF) reveal its liquid phase is dominated by a cyclic trans-NMF pentamer. This study uniquely considers cis-trans isomerism and improves binary mixture modeling.
Area of Science:
- Computational Chemistry
- Physical Chemistry
- Chemical Physics
Background:
- The quantum cluster equilibrium (QCE) approach models liquid phases using gas-phase-like clusters.
- Accurate modeling of binary mixtures and isomerism remains challenging for QCE.
Purpose of the Study:
- To refine the QCE method for improved accuracy in modeling N-methylformamide (NMF) and its aqueous solutions.
- To explicitly incorporate cis-trans isomerism of NMF within the QCE framework.
- To accurately describe the thermodynamic properties of NMF and its binary mixtures.
Main Methods:
- A refined QCE approach with separate iterative cycles for gas and liquid phases.
- Density Functional Theory (DFT) for cluster geometries and frequencies, benchmarked with coupled cluster (CC) single point energies.
- Explicit consideration of NMF cis-trans isomerism and mean-field interactions.
Main Results:
- The refined QCE method successfully models NMF and its aqueous solution, avoiding metastable states.
- The liquid phase of neat NMF is predominantly composed of a cyclic trans-NMF pentamer.
- Accurate thermodynamic description requires a large set of clusters, irrespective of the quantum chemical method used.
Conclusions:
- The refined QCE approach provides a robust method for studying liquid phase properties and binary mixtures.
- The cyclic trans-NMF pentamer is identified as the key structural motif in neat NMF liquid.
- Explicit consideration of isomerism is crucial for accurate QCE modeling of molecular liquids.
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