Hydrogen-bond structure and low-frequency dynamics of electrolyte solutions: Hydration numbers from ab Initio water reorientation dynamics and dielectric relaxation spectroscopy

Seonmyeong Kim, Xiangwen Wang, Jeongmin Jang, Kihoon Eom, Simon L Clegg, Gun-Sik Park, Devis Di Tommaso

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)
18 Downloads (Pure)


We present an atomistic simulation scheme for the determination of the hydration number (h) of aqueous electrolyte solutions based on the calculation of the water dipole reorientation dynamics. In this methodology, the time evolution of an aqueous electrolyte solution generated from ab initio molecular dynamics simulations is used to compute the reorientation time of different water subpopulations. The value of h is determined by considering whether the reorientation time of the water subpopulations is retarded with respect to bulk-like behavior. The application of this computational protocol to magnesium chloride (MgCl2 ) solutions at different concentrations (0.6-2.8 mol kg-1 ) gives h values in excellent agreement with experimental hydration numbers obtained using GHz-to-THz dielectric relaxation spectroscopy. This methodology is attractive because it is based on a well-defined criterion for the definition of hydration number and provides a link with the molecular-level processes responsible for affecting bulk solution behavior. Analysis of the ab initio molecular dynamics trajectories using radial distribution functions, hydrogen bonding statistics, vibrational density of states, water-water hydrogen bonding lifetimes, and water dipole reorientation reveals that MgCl2 has a considerable influence on the hydrogen bond network compared with bulk water. These effects have been assigned to the specific strong Mg-water interaction rather than the Cl-water interaction.

Original languageEnglish
Pages (from-to)2334-2346
Number of pages13
Issue number20
Early online date31 Aug 2020
Publication statusPublished - 16 Oct 2020


  • ab initio molecular dynamics
  • dielectric relaxation spectroscopy
  • electrolyte solutions
  • hydration number
  • water orientational dynamics

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