Solvent dynamical effects in electron transfer: molecular dynamics simulations of reactions in methanol

Phelps, Donald K.; Weaver, Michael J.; Ladanyi, Branka M.

doi:10.1016/0301-0104(93)80262-8

Cited by 50 publications

(33 citation statements)

References 56 publications

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“…20 Thus, the reason for the breakdown of LR is not the lack of effectiveness of inertial translational motions in causing relaxation, as would be suggested by previous work. [5][6][7][8] Rather, the LR approximation fails because the perturbations in nonpolar solvation are extremely shortrange. What we will argue is that, with only a few molecules strongly coupled, the inertial solvent translations that are present at equilibrium are not the motions that cause relaxation during nonequilibrium dynamics, leading to the failure of LR for nonpolar solvation dynamics.…”

Section: Breakdown Of Linear Response For Nonpolar Solvationmentioning

confidence: 99%

“…Yet, in nearly every computer simulation study of solvation dynamics (but not all [5][6][7][8] ), the LR assumption of eq 2 is able to predict, remarkably well, the majority of the nonequilibrium response, eq 1, when the solute undergoes a change in charge distribution. [9][10][11][12][13][14][15][16] The agreement is good enough that many recent studies have chosen to forego the computation of nonequilibrium trajectories and base their conclusions solely on predictions from the LR approximation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

2000

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The fact that the motion of solvent molecules defines the reaction coordinate for electron-transfer and other chemical reactions has generated great interest in solvation dynamics, the study of how the solvent responds to changes in a solute's electronic state. In the limit of linear response (LR), when the perturbation caused by the solute is "small", the relaxation of the excited solute's energy gap should behave identically to the relaxation dynamics of the unperturbed solute following a natural fluctuation of the gap away from equilibrium. Despite the fact that the addition of a fundamental unit of charge to a small solute results in a solvation energy that is tens or hundreds of kT, computer simulations of solvation dynamics have found, with only a few exceptions, that LR is obeyed for changes in solute charge. Essentially none of this work, however, accounts for the fact that the solutes in real chemical reactions undergo changes in size and shape as well as in charge distribution. In this paper, we compare the results of molecular simulations of polar and nonpolar solvation dynamics for a simple Lennard-Jones solute in a flexible-water solution to explore the validity of LR. We find that, when short-range forces are involved, LR breaks down dramatically: both the inertial and diffusive components of the relaxation differ from those predicted by LR. For increases in solute size, expansion of the solute drives the first-shell solvent molecules into the second shell. The resulting nonequilibrium relaxation takes advantage of translation-rotation coupling that does not occur at equilibrium, resulting in faster solvation than that predicted by LR. Decreases in solute size, on the other hand, result in inward translational motions of solvent molecules that affect the solute's energy gap by destabilizing the energy of the (unoccupied) ground state. The inward motions involved in the nonequilibrium relaxation are not present at equilibrium because the destabilization of the ground state is much larger than kT. Because the energetically most important solvent molecules, those closest to the solute, are just as likely to be moving away from the solute as toward it at the time of excitation, solvation for decreases in size is much slower than predicted by LR. In the most realistic cases, when both the size and the charge of the solute change, the solvent translational motions resulting from the size change and those resulting from electrostriction, the net ion-dipole attraction between the charged solute and the polar solvent, combine in an additive fashion. When the solute both gains a charge and expands, the translational motions resulting from electrostriction nearly cancel those from the outward solute expansion so that rotational motions dominate the solvent response; the small net expansion that remains results in only a minor breakdown of LR. The additional inward solvent translations beyond those required by electrostriction, which are necessary when the solute becomes charged and its size decreases, on the ...

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Section: Breakdown Of Linear Response For Nonpolar Solvationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

2000

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“…Most of MD simulations were only concerned with modelling of solvent relaxation after instantaneous photoexcitation of various species. There were, however, several ET-MD works published [5,10,11,16,18]. Bader and Chandler [11] studied a realistic model of aqueous ferric-ferrous system, on the other hand, Phelps et al [18] used a more general model of electron transfer reactions in methanol approximating reactants by a pair of Lennard-Jones spheres in contact of varying diameter and containing a univalent charge.…”

Section: Numerical Calculations and Discussionmentioning

confidence: 99%

“…During the last few years the very large evidence on solvation dynamics in polar solvents has been acquired [8] by means of the molecular dynamics (MD) computer experiments in water [9][10][11][12][13][14], solvent resembling methyl chloride [15,16], acetonitrile [17] and methanol [18][19][20]. In acetonitrile (no hydrogen bonding), the initial Gaussian decay of Δ(t) constitutes 70-80% of the total relaxation and occurs on a time scale of 100-250 fs.…”

Section: Introductionmentioning

confidence: 99%

Role of Inertial Effects in Electron Transfer Kinetics

Gajdek

1996

Acta Phys. Pol. A

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The electron transfer rates at the steady state are evaluated in terms of the Gaussian wave packet motion on free energy curves in the two-and three-surface models in the presence of inertial effects. The autocorrelation functions of the solvent polarization coordinate are fitted to the results of recent molecular dynamics simuJations. It is found that the inertial effects are particularly important for the electron transfer processes in acetontrile and water. They constitute an impeding factor in the wave packet motion. The neglect of the inertial part of the solvent autocorrelation function gives underestimation of the electron transfer rate coefficient.

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“…17,18,[21][22][23][24][25][26][27][28][29][30] However, multiple long trajectories are required to perform umbrella sampling, making it impractical to perform calculations for general solvents. Integral-equation theories [31][32][33][34][35][36][37][38] are a more convenient alternative to the laborious nonequilibrium sampling schemes in MD simulations, but nanosecond MD simulations are still required to compute the solvent correlation functions in these approaches.…”

Section: Introductionmentioning

confidence: 99%

A molecularly based theory for electron transfer reorganization energy

Zhuang

Wang

2015

The Journal of Chemical Physics

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Articles you may be interested inUsing field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule's permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory. C 2015 AIP Publishing LLC. [http://dx

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Solvent dynamical effects in electron transfer: molecular dynamics simulations of reactions in methanol

Cited by 50 publications

References 56 publications

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

Role of Inertial Effects in Electron Transfer Kinetics

A molecularly based theory for electron transfer reorganization energy

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