title: Closed-form expressions of quantum electron transfer rate based on the stationary-phase approximation.
abstract: Closed-form rate expressions are derived on the basis of the stationary-phase approximation for the Fermi golden rule expression of the quantum electron-transfer (ET) rate. First, on the basis of approximate solutions of the stationary-phase points near DeltaG = 0, -lambda, and lambda, where DeltaG is the reaction free energy and lambda is the reorganization energy, three closed-form rate expressions are derived, which are respectively valid near each value of DeltaG. Numerical tests for a model Ohmic spectral density with an exponential cutoff demonstrate good performance of the derived expressions in the respective regions of their validity. In particular, the expression near DeltaG = -lambda, which differs from the semiclassical approximation only by a prefactor quadratic in DeltaG, works substantially better than the latter. Then, a unified formula is suggested, which interpolates the three approximate expressions and serves as a good approximation in all three regions. We have also demonstrated that the interpolation formula can serve as a good quantitative means for understanding the temperature dependence of the quantum ET rate.
authors.affiliation: Department of Chemistry and Biochemistry, Queens College and Graduate Center of the City University of New York, 65-30 Kissena Boulevard, Flushing, New York 11367, USA. Seogjoo.Jang@qc.cuny.edu
authors.forename: Seogjoo
authors.initials: S
authors.lastname: Jang
authors.forename: Marshall D
authors.initials: MD
authors.lastname: Newton