Probing the Ion-Specific Effects at the Water/Air Interface and Water-Mediated Ion Pairing in Sodium Halide Solution with Ab Initio Molecular Dynamics

Jinfeng Liu, John Z.H. Zhang, Xiao He

Research output: Contribution to journalArticle


The ion-specific effects at the water/air interface represent a fundamentally essential topic of research, and high-level ab initio simulations are still demanding to reveal the microscopic picture of the interactions between ions and water at the solvation interface. In this work, we present a fragment-based ab initio molecular dynamics (AIMD) simulation of sodium halide solution droplet (in a neutral mixture of Na+, F-, Cl-, and Br- ions) at the MP2/aug-cc-pVDZ level. We show that the studied halide ions exhibit surface preference in the order (F- < Cl- < Br-) which is in accordance with the experimental observation. The resulting potential of mean force (PMF) for Br- produces a distinct minimum at the water/air interface, while the minimum of the PMF for F- appears in the bulk region. The ion-pairing interactions between halide anions and Na+ cations are characterized, and it reveals that the specific solvent-separated ion pairs (SIPs) are more preferred than the direct contact ion pairs (CIPs). The transition between different types of SIPs is observed. Other structural and dynamical properties of ions and ion-hydration shells are investigated. These results provide broader and new physical insights for understanding the ion-specific behavior in interfacial solvation at the atomistic level.

Original languageEnglish (US)
Pages (from-to)10202-10209
Number of pages8
JournalJournal of Physical Chemistry B
Issue number44
StatePublished - Nov 8 2018


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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