An analysis of hydrated proton diffusion in ab initio molecular dynamics

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Dynamics

Background:

• Proton transport in aqueous systems is fundamental but involves complex, multiscale phenomena.
• Understanding molecular mechanisms of long-range proton migration and burst-and-rest dynamics remains challenging.
• The role of hydrogen bonding and water structure in proton mobility requires further investigation.

Purpose of the Study:

• To investigate the molecular mechanisms underlying proton transport in water.
• To identify factors correlating with burst-and-rest proton dynamics.
• To explore the influence of temperature and hydrogen bonding on proton migration.

Main Methods:

• Utilized extensive ab initio molecular dynamics (AIMD) simulations (∼2.7 ns).
• Employed various density functional approximations (e.g., BLYP, B3LYP) and temperatures (300-330 K).
• Analyzed equilibrium and dynamical properties of excess protons in a water cluster.

Main Results:

• Identified concerted hops and weak hydrogen-bond donors as key features influencing proton dynamics.
• Found strong correlation between hydrogen bond presence/absence with a fourth water molecule and burst/rest dynamics.
• Observed low probability for a fourth water molecule to approach hydronium, suggesting stable void formation.

Conclusions:

• Weak hydrogen bonds from neighboring water molecules are strongly linked to burst-and-rest proton dynamics.
• Pre-solvation concepts are consistent with observed correlations in proton hopping events.
• Temperature influences structural and dynamical properties of proton transport in water.