During precipitation of NaCl in the presence of several impurities, light is emitted in the blue/UV part of the spectrum. This phenomenon is known as crystalloluminescence. As a first step to understand this highly complex process we focus on the characterization of charge distributions in concentrated solutions since charge transfer is very likely involved in the mechanism of crystallization. Five different concentrations of aqueous NaCl (1M, 2M, 4M, 5.2M and 6.7M) have been simulated with CP2K using classical dynamics and then resampled using BLYP DFT. Additionally, three different charge analysis methods (Bader, ChelpG and Mulliken) were tested on the ground and excited states, using high-level MRCISD calculations, of the gas phase NaCl dissociation curve to serve as benchmarks for the condensed phase simulations. We find that Bader analysis is able to predict charges with an accuracy of 0.1e while yielding the correct sign of the charges on both ground and excited states. To obtain the charges for the condensed phase aqueous electrolytes, snapshots from the ab initio resampled trajectories were used to obtain electron densities for Bader analysis. The Na+ show a narrow distribution around 0.905 e and are independent of concentration whereas the Cl- show charges ranging from -0.65 to -0.85 dependent on concentration. As a result of this charge asymmetry, the H2O molecules acquire a slight negative charge and thus act as an electronic sink.

Towards charge characterization of Na and Cl ions in ground and excited states in aqueous electrolytes

246th National Meeting (2013)

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