Daub CD, Hänninen V, Halonen L. Ab Initio Molecular Dynamics Simulations of the Influence of Lithium Bromide on the Structure of the Aqueous Solution-Air Interface.
J Phys Chem B 2019;
123:729-737. [PMID:
30605330 PMCID:
PMC6727360 DOI:
10.1021/acs.jpcb.8b10552]
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Abstract
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We
present the results of ab initio molecular dynamics simulations
of the solution–air interface of aqueous lithium bromide (LiBr).
We find that, in agreement with the experimental data and previous
simulation results with empirical polarizable force field models,
Br– anions prefer to accumulate just below the first
molecular water layer near the interface, whereas Li+ cations
remain deeply buried several molecular layers from the interface,
even at very high concentration. The separation of ions has a profound
effect on the average orientation of water molecules in the vicinity
of the interface. We also find that the hydration number of Li+ cations in the center of the slab Nc,Li+–H2O ≈ 4.7 ±
0.3, regardless of the salt concentration. This estimate is consistent
with the recent experimental neutron scattering data, confirming that
results from nonpolarizable empirical models, which consistently predict
tetrahedral coordination of Li+ to four solvent molecules,
are incorrect. Consequently, disruption of the hydrogen bond network
caused by Li+ may be overestimated in nonpolarizable empirical
models. Overall, our results suggest that empirical models, in particular
nonpolarizable models, may not capture all of the properties of the
solution–air interface necessary to fully understand the interfacial
chemistry.
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