Microscopic description of acid-base equilibrium.

Area of Science:

• Chemical Physics
• Computational Chemistry
• Physical Chemistry

Background:

• Acid-base reactions are fundamental chemical processes with broad implications across scientific disciplines.
• Experimental methods often lack the resolution to fully elucidate the molecular mechanisms of these reactions.
• Atomistic simulations offer a complementary approach to gain insights into microscopic behaviors.

Purpose of the Study:

• To develop and validate a new computational methodology for simulating acid-base reactions.
• To investigate the molecular mechanisms of proton transfer in aqueous solutions.
• To provide a simulation framework that complements experimental findings.

Main Methods:

• Ab initio molecular dynamics (MD) simulations were employed to model the systems.
• Metadynamics, an enhanced sampling technique, was utilized to overcome large free-energy barriers.
• Novel descriptors or collective variables (CVs) were introduced for enhanced sampling of acid-base equilibria.

Main Results:

• The developed simulation approach successfully captured the dynamics of acid-base reactions.
• Proton dissociation and transfer mechanisms were investigated at the atomistic level.
• The method was validated using representative aqueous solutions of acetic acid, ammonia, and bicarbonate.

Conclusions:

• The combination of ab initio MD and metadynamics with novel CVs provides a powerful tool for studying acid-base reactions.
• This computational strategy offers valuable insights into molecular mechanisms that are difficult to obtain experimentally.
• The approach is applicable to a range of acid-base behaviors, including acidic, basic, and amphoteric systems.