Correlated dynamics in aqueous proton diffusion.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• The diffusion of protons in aqueous solutions is significantly higher than other ions.
• The Grotthuss mechanism, involving proton hopping between water molecules, is the accepted explanation for this high mobility.
• Current interpretations of experimental data rely on the assumption of equal hopping probabilities.

Purpose of the Study:

• To investigate the hopping probabilities of protons in water using computational simulations.
• To challenge the assumption of uniform proton hopping in the Grotthuss mechanism.
• To re-evaluate the timescale of the Grotthuss mechanism based on simulation findings.

Main Methods:

• Ab initio molecular dynamics simulations were employed.
• Analysis focused on the probability distribution of proton hops between neighboring water molecules.
• Correlations in proton hopping events were examined.

Main Results:

• Simulations revealed that protons do not hop with equal probability to all neighboring water molecules.
• An increased probability for protons to revert to their previous location was observed.
• These findings indicate a deviation from the standard assumption in Grotthuss mechanism studies.

Conclusions:

• The assumption of equal proton hopping probabilities in the Grotthuss mechanism is not universally valid.
• Experimental data interpretations may need revision based on these simulation results.
• The effective timescale of the Grotthuss mechanism is likely shorter than previously estimated.