Free energy functionals for polarization fluctuations: Pekar factor revisited

Journal Article · Mon Feb 13 00:00:00 EST 2017 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4975625· OSTI ID:1340505

Dinpajooh, Mohammadhasan ^[1]; Newton, Marshall D. ^[2]; Matyushov, Dmitry V. ^[3]

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1. School of Molecular Sciences, Arizona State University, P.O. Box 871604, Tempe, Arizona 85287-1604, USA; Arizona State University
2. Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973-5000, USA
3. Department of Physics and School of Molecular Sciences, Arizona State University, P.O. Box 871504, Tempe, Arizona 85287-1504, USA

The separation of slow nuclear and fast electronic polarization in problems related to electron mobility in polarizable media was considered by Pekar 70 years ago. Within dielectric continuum models, this separation leads to the Pekar factor in the free energy of solvation by the nuclear degrees of freedom. The main qualitative prediction of Pekar’s perspective is a significant, by about a factor of two, drop of the nuclear solvation free energy compared to the total (electronic plus nuclear) free energy of solvation. The Pekar factor enters the solvent reorganization energy of electron transfer reactions and is a significant mechanistic parameter accounting for the solvent effect on electron transfer. Here, we study the separation of the fast and slow polarization modes in polar molecular liquids (polarizable dipolar liquids and polarizable water force fields) without relying on the continuum approximation. We derive the nonlocal free energy functional and use atomistic numerical simulations to obtain nonlocal, reciprocal space electronic and nuclear susceptibilities. A consistent transition to the continuum limit is introduced by extrapolating the results of finite-size numerical simulation to zero wavevector. The continuum nuclear susceptibility extracted from simulations is numerically close to the Pekar factor. However, we derive a new functionality involving the static and high-frequency dielectric constants. The main distinction of our approach from the traditional theories is found for the solvation free energy due to the nuclear polarization: the anticipated significant drop of its magnitude with increasing liquid polarizability does not occur. The reorganization energy of electron transfer is either nearly constant with increasing the solvent polarizability and the corresponding high-frequency dielectric constant (polarizable dipolar liquids) or actually noticeably increases (polarizable force fields of water).

• Research Organization: Arizona State Univ., Tempe, AZ (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: SC0015641
• OSTI ID: 1340505
• Alternate ID(s): OSTI ID: 1349561; OSTI ID: 1361771
• Report Number(s): BNL--113669-2017-JA
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 6 Vol. 146; ISSN JCPSA6; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY