Steady state current transfer and scattering theory

The correspondence between the steady state theory of current transfer and scattering theory in a system of coupled tight-binding models of 1-dimensional wires is explored. For weak interwire coupling both calculations give nearly identical results, except at singular points associated with band edges. The effect of decoherence in each of these models is studied using a generalization of the Liouville-von Neuman equation suitable for steady-state situations. An example of a single impurity model is studied in details, leading to a lattice model of scattering off target that affects both potential scattering and decoherence. For an impurity level lying inside the energy band, the transmission coefficient diminishes with increasing dephasing rate, while the opposite holds for impurity energy outside the band. The efficiency of current transfer in the coupled wire system decreases with increasing dephasing.Comment: 22 pages, 13 figure

Steady state theory of current transfer

Current transfer is defined as a charge transfer process where the transferred charge carries information about its original motion. We have recently suggested that such transfer causes the asymmetry observed in electron transfer induced by circularly polarized light through helical wires. This paper presents the steady state theory of current transfer within a tight binding model of coupled wires systems. The efficiency of current transfer is quantified in terms of the calculated asymmetry in the system response to a steady current imposed on one of the wires, with respect to the imposed current direction.Comment: 25 pages, 14 figure

Low Temperature Electronic Transport through Macromolecules and Characteristics of Intramolecular Electron Transfer

A theory of electronic transport through molecular wires is applied to analyze characteristics of a long-range electron transfer (ET) through molecular bridges in macromolecules with complex donor/acceptor subsystems. Assuming a coherent electron tunneling through the bridge to be the predominant mechanism of ET at low temperatures it is shown that low temperature current-voltage curves can exhibit a step-like structure, which contains information concerning intrinsic features of ET processes such as the effect of donor/acceptor coupling to the bridge and primary pathways of electrons tunneling through the bridge. By contacting the proposed theoretical analysis with such experimental data a variety of valuable characteristics of long-range intramolecular ET can be identified. Analytical and numerical results are presented. Using the Buttiker dephasing model within the scattering matrix formalism we analyze dephasing effects, and we show that these effects could be reduced enough to allow the structure of the electron transmission function to be exposed in the experiments on the electronic transport through macromolecules.Comment: 9 pages, 2 figures, text revise

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH−-containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH−, upon photo-excitation of FADH− with 350–450 nm light. We compute the lowest singlet excited states of FADH− in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH− that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron- acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH− - thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green’s function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH− causes a π → π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH− - to - dimer electronic coupling, thus inducing rapid electron transfer

Quantum dynamics in strong fluctuating fields

A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. Herein, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis the influence of nonequilibrium fluctuations and periodic electrical fields on quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.Comment: review article, Advances in Physics (2005), in pres

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]