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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 15: Poster Session I

CPP 15.71: Poster

Montag, 17. März 2025, 19:00–21:00, P4

Evidence for unusual solvation shell of aqueous Fe³⁺ at high dilution — •Amrita Goswami, Elvar Örn Jónsson, and Hannes Jónsson — Science Institute and Faculty of Physical Sciences, University of Iceland, VR-III, 107 Reykjavík, Iceland

Solvated Fe³⁺ in water is a particularly important system, relevant, for instance, for the widely studied charge transfer Fe3+/Fe2+. However, the solvation shell of such highly charged cations is still poorly understood, particularly at for concentrations less than 1 M. In this regime of high dilution, experimental data and high-level calculations are sparse. For instance, most density-functional theory calculations are performed at a concentration of 0.8 M or higher, with uniform background charge. Simulations for such dilute solutions can provide insight inaccessible to other techniques. Using extensive molecular dynamics simulations with empirical potentials and DFT geometry optimizations of selected configurations, we study the effect of solution concentration on the solvation structure of aqueous Fe³⁺. The solvation shell is found to undergo abrupt transitions between two states: an octahedral (OH) state with 6-fold coordination, and a metastable capped trigonal prism (CTP) state with 7-fold coordination. Further, we have developed a QM/MM (quantum-mechanical/molecular mechanical) method to study dilute solutions of aqueous Fe³⁺ with DFT-level accuracy, with a polarizable water model. References: Goswami et al., J. Phys. Chem. Lett., 2024

Keywords: solvation; QM/MM; density functional theory; solvated ions