Free energy functionals for polarization fluctuations: Pekar factor revisited.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Pekar's theory (70 years ago) separated electronic and nuclear polarization for electron mobility in polarizable media.
• This separation introduced the Pekar factor, predicting a significant drop in nuclear solvation free energy.
• The Pekar factor is crucial for understanding solvent effects on electron transfer reactions.

Purpose of the Study:

• To investigate the separation of fast electronic and slow nuclear polarization modes in polar molecular liquids.
• To move beyond the continuum approximation by using atomistic simulations.
• To derive a nonlocal free energy functional and analyze solvation free energy and electron transfer reorganization energy.

Main Methods:

• Development of a nonlocal free energy functional.
• Atomistic numerical simulations to compute electronic and nuclear susceptibilities in reciprocal space.
• Extrapolation of finite-size simulation results to the continuum limit (zero wavevector).

Main Results:

• The continuum nuclear susceptibility from simulations aligns with the Pekar factor.
• A new functionality involving static and high-frequency dielectric constants was derived.
• Contrary to Pekar's prediction, nuclear solvation free energy does not significantly drop with increasing liquid polarizability.

Conclusions:

• Electron transfer reorganization energy remains constant or increases with solvent polarizability, challenging traditional theories.
• The study provides a more accurate, simulation-based understanding of polarization effects in polar liquids.
• Findings impact the mechanistic understanding of electron transfer in various solvent environments.