Charge and Electric Field Fluctuations in Aqueous NaCl Electrolytes
Conventional wisdom concerning crystallization assumes that when NaCl crystallizes from a supersaturated solution, the solvated ions retain their ionic character and simply relocate from their hydration spheres to their most stable positions in the crystal lattice. However, this conventional picture is at odds with observations over 200 years ago reporting the emission of long-lived light resulting from the crystallization of certain salts – appropriately referred to as crystalloluminescence. This suggests that electronic structure plays an essential role in crystallization. Strong electric field fluctuations in the gas or condensed phases can drive changes in electronic structure. We have calculated the fluctuation of charge, scalar electric potentials, and vector electric fields for concentrated aqueous NaCl electrolytes. The H2O molecules in the 1st solvation shell of the ions serve as a sink for electron density originating on Cl-. Our analysis reveals that the electric fields inside aqueous electrolytes are extremely large (up to several V/Å) and thus may alter the ground and excited electronic states in the condensed phase. Furthermore, our analysis shows that the potential and field distributions are largely independent of concentration. We find that the field component distributions to be Gaussian for the ions and non-Gaussian for the O and H sites (computed in the lab frame of reference), however, these non-Gaussian distributions are readily modeled via an orientationally averaged non-zero mean Gaussian plus a zero mean Gaussian. These calculations and analyses provide the first steps toward understanding the magnitude and fluctuations of charge, electric potentials and fields in aqueous electrolytes and what role these fields may play in driving charge redistribution/transfer during crystalloluminescence. We would like to gratefully acknowledge helpful discussions with Gregory K. Schenter. This work was supported by the U.S. Department of Energy’s (DOE) Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences program and used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Pacific Northwest National Laboratory (PNNL) is operated by Battelle for the US Department of Energy.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1130709
- Report Number(s):
- PNNL-SA-96493; KC0301020
- Journal Information:
- Journal of Physical Chemistry B, 117(37):10869-10882, Journal Name: Journal of Physical Chemistry B, 117(37):10869-10882
- Country of Publication:
- United States
- Language:
- English
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