Unbiased charge oscillations in B-DNA: Monomer polymers and dimer polymers

Abstract

We call monomer a B-DNA base-pair and examine, analytically and numerically, electron or hole oscillations in monomer-and dimer-polymers, i.e., periodic sequences with repetition unit made of one or two monomers. We employ a tight-binding (TB) approach at the base-pair level to readily determine the spatiotemporal evolution of a single extra carrier along a N base-pair polymer. We study HOMO and LUMO eigenspectra as well as the mean over time probabilities to find the carrier at a particular monomer. We use the pure mean transfer rate k to evaluate the easiness of charge transfer. The inverse decay length β for exponential fits k(d), where d is the charge transfer distance, and the exponent η for power law fits k(N ) are computed; generally power law fits are better. We illustrate that increasing the number of different parameters involved in the TB description, the fall of k(d) or k(N ) becomes steeper and show the range covered by β and η. Finally, both for the time-independent and the time-dependent problem, we analyze the palindromicity and the degree of eigenspectrum dependence of the probabilities to find the carrier at a particular monomer.

Electronic structure and carrier transfer in B-DNA monomer polymers and dimer polymers: Stationary and time-dependent aspects of a wire model versus an extended ladder model

“…1 we present the calculated HOMO/LUMO eigenspectra for an example of type α ′ polymers, poly(dA)-poly(dT). For TB I, an analytical expression can also be found for the eigenvectors 18 . The eigenvectors (hence, the occupation probabilities, too) are eigenspectrum independent 18 , i.e., they do not depend on the TB parameters E bp , t bp .…”

“…For TB I, an analytical expression can also be found for the eigenvectors 18 . The eigenvectors (hence, the occupation probabilities, too) are eigenspectrum independent 18 , i.e., they do not depend on the TB parameters E bp , t bp . Furthermore, the occupation probabilities display palindromicity 18 , i.e., the occupation probability of each eigenstate of the µ-th monomer is equal to that of the (N − µ + 1)-th monomer (…”

“…For TB I, an analytical expression for the eigenvalues of type α ′ polymers exists 18 . All eigenvalues are symmetric around the on-site energy E bp of the monomers and lie in the interval E bp − 2 t bp , E bp + 2 t bp .…”

“…For TB I, analytical expressions for the eigenvalues of type β ′ polymers with N odd exist 18 . For N odd the eigenvalues can be expressed explicitly in terms of Chebyshev zeros 44 .…”

“…The carriers (electrons or holes) can be either inserted via electrodes or generated by UV irradiation and by chemical reduction or oxidation. Moreover, although unbiased charge transfer in DNA nearly vanishes after 10 to 20 nm 17,18 , DNA still remains a promising candidate as an electronic component in molecular electronics, e.g. as a short molecular wire 19 .…”