A note on the mechanism of charge transport at different temperatures in aperiodic nucleotide base-stacks

Abstract

After calculating the electronic density of states (DOS) using the matrix block negative factor counting method, the Anderson localization of the physically interesting states of periodic nucleotide base stacks were calculated. After that (applying the inverse iteration procedure) hopping frequencies and finally (using a random walk theory) the high-frequency hopping conductivity, | σ( ω)| of the aperiodic base stacks were computed in the temperature range T=60 K– T=320 K. The results obtained are in good agreement with recent electron energy loss experiments in a hole resonator. From the temperature dependence of | σ( ω)| the activation energy of the conductivity was determined. At T=70 K Δ E≈0.004 eV and with increasing T it increases until 0.160 eV at 120 K in the case of the frequency of ω=10 11 s −1. At still larger temperatures it slowly decreases until ∼0.114 eV at ∼310 K. These results can be interpreted that at T=70 K multichannel tunneling is the dominant mechanism. With increasing T higher lying tunneling levels are reached. The increase of the energy of the tunneling levels causes the increase of | σ( ω)| with the temperature. If T>80 K the dominant mechanism becomes variable range hopping which is indicated by the simultaneous steep rise of both Δ E and | σ( ω)|. If T>120 K the barrier height decreases accompanied by further sharp increase of | σ( ω)|. This decrease of Δ E at larger T values can be interpreted that in these cases also higher lying levels become populated. Finally this contributes also to the increase of the Boltzmann factors and with it to the increase of the hopping conductivity.