We propose a model Hamiltonian for describing charge transport through short homogeneous double stranded DNA molecules. We show that the hybridization of the overlapping orbitals in the base-pair stack coupled to the backbone is sufficient to predict the existence of a gap in the nonequilibrium current-voltage characteristics with a minimal number of parameters. Our results are in a good agreement with the recent finding of semiconducting behavior in short poly(G)-poly(C) DNA oligomers. In particular, our model provides a correct description of the molecular resonances which determine the quasilinear part of the current out of the gap region. DOI: 10.1103/PhysRevB.65.241314 PACS number͑s͒: 72.80.Le, 05.60.Ϫk, 87.10.ϩe, 87.14.Gg The attempt to understand the mechanism of electron motion along DNA is the source of an intense debate in the biochemical and chemical physics communities. 1 Solving this problem is an essential step for the development of DNA-based molecular electronics. New insights to this issue are brought by recent breakthroughs in direct measurements through DNA molecules. 2-8 Transport measurements through nanostructured systems are potentially capable of addressing the basic issues of the conduction properties of molecular and supramolecular aggregates. The aftermath for the realization of molecular electronics devices is straightforward. 9 It is thus not surprising that DNA molecules became the subject of an intense study concerning their potency to carry an electric current, 2-7 and to provide a scaffold for the metal assembling of highly conductive nanowires. 4,8 From a nanoelectronics perspective, the DNA possesses ideal structural and molecular-recognition properties, and the understanding of the charge transport through DNA may result in the ambitious goal of self assembling nanodevices with a definite molecular architecture. 10 The hypothesis that double stranded DNA supports charge transport as a linear chain of overlapping orbitals located on the stacked base pairs, already advanced in the early sixties, 11 received first experimental boosts only recently via long-range electron transfer measurements. 12 As far as transport through DNA is concerned, the available experiments are still controversial mainly due to the complexity of the environment and the molecule itself ͑sequence variability, 13 thermal vibrations . . . ). Concerning theory, the most reliable procedure to tackle these systems would be the ab initio quantum chemistry approach. However, massive numerical costs complicate its use for realistic biological systems. 14 To our knowledge, at the present time, only few densityfunctional-theory ͑DFT͒ calculations for DNA molecules are available. 7,15 In a parallel development particular aspects of the DNA transport phenomenology have been explained as mediated by polarons, 16 solitons, 17 electrons or holes. 1,18 Such lack of a unifying theoretical scheme calls for reproducible and unambiguous experimental results that are still a great technological challenge.Recently, Porath ...

A detailed study of electronic phase transitions in the ionic Hubbard model at half filling is presented. Within the dynamical mean field approximation a series of transitions from the band insulator via a metallic state to a Mott-Hubbard insulating phase is found at intermediate values of the one-body potential ∆ with increasing the Coulomb interaction U . We obtain a critical region in which the metallic phase disappears and a novel coexistence phase between the band and the Mott insulating state sets in. Our results are consistent with those obtained at low dimensions, thus they provide a concrete description for the charge degrees of freedom of the ionic Hubbard model. PACS numbers: 71.10.Hf, 71.27.+a, 71.30.+h One important problem in the field of electronic structure theory is the understanding of the Mott metalinsulator transition (MIT).1,2 Many details have already been clarified using the canonical model for this transition -the one-band Hubbard model. At half filling (i.e., having in average one electron at each lattice site) this transition from the metallic to the Mott-Hubbard insulating (MI) phase occurs with increasing the on-site repulsion U . Great progress in understanding the MIT in Hubbard-like models has been achieved in the last decade with the development of the dynamical mean field theory (DMFT). Although many aspects of the coherent (Fermi liquid) metallic phase and the incoherent MI phase are now quite well understood, other questions remain open, especially the relationship between the MI regime and band insulators (BI), where one sub-band is almost completely filled by two electrons such that an excitation gap is formed.To study the interplay between band and MottHubbard insulators, various extended versions of the oneband Hubbard model have been proposed. It is remarkable that different models show separate kinds of behavior. Some of them have a crossover from the BI to the MI regime, 3 whereas others have clear transition points with a metallic phase in between.4 A widely studied model for the second class is the ionic Hubbard model (IHM). 5,6,7In the one-dimensional (1D) IHM, however, a ferroelectric (or bond-ordered) phase is realized which separates BI and MI, and the metallic phase shrinks to only one point.10,11 Already in 1D, a finite metallic region can be recovered by introducing an intra-sublattice hopping t ′ into the IHM.12 In 2D 7 or at larger dimensions 5 a correlation induced metallic phase was reported between BI and MI, but it is still under debate whether this metallic phase shrinks to a line 5 or if it ends up at certain particular point by increasing the ionicity ∆. In this work we show that the metallic phase disappears at a certain value of ∆ above which we found a coexistence region composed of distinct insulating phases.It might be not very surprising to find quite different behavior in various models at different dimensions. But even if we restrict our attention to the IHM, the phase diagram is highly disputed. The 2D case was studied by a cluster extension...

We present a detailed description for the metal-insulator transition in paramagnetic VO 2 . Based on recent experimental data we show the importance of multiorbital electron-electron interactions along with firstprinciples band structure data for a consistent description of the metal-insulator transition in this system. Using the local-density approximation ͑LDA͒ϩdynamical mean field ͑DMFT͒ multiorbital iterated-perturbation theory scheme, which merges the LDA with DMFT, we show that the metal-insulator transition is accompanied by a large spectral weight transfer due to changes in the orbital occupations. Within this scenario we find good agreement with the one-electron spectral function in the metallic phase of VO 2 . We also compare our results for the total spectral density with other approaches which use the quantum Monte Carlo method to solve the impurity problem of DMFT.

We describe the correlated electronic structure of a prototype Fe-pnictide superconductor, SmO1−xFxFeAs, using LDA+DMFT. Strong, multi-orbital electronic correlations generate a lowenergy pseudogap in the undistorted phase, giving a bad, incoherent metal in qualitative agreement with observations. Very good semi-quantitative agreement with the experimental spectral functions is seen, and interpreted, within a correlated, multi-orbital picture. Our results show that Fe-pnictides should be understood as low-carrier density, incoherent metals, in resemblance to the underdoped cuprate superconductors. PACS numbers: 71.27.+a, 74.25.Jb, Discovery of high-T c superconductivity (HTSC) in the Fe-based pnictides [1] is the latest among a host of other, ill-understood phenomena in d-band oxides. HTSC in Fe-pnictides emerges upon doping a bad metal with spin density wave (SDW) order at q = (π, 0). Preliminary experiments indicate [2, 3] unconventional SC. Existent normal state data indicate a "bad metal" without Landau Fermi Liquid (FL) quasiparticles at low energy [1]. These observations in Fe-pnictides are reminiscent of cuprate SC. The small carrier density (giving rise to carrier pockets), along with Uemura scaling from µ-SR [4] similar to hole-doped cuprates strongly suggests a SC closer to the Bose condensed, rather than a BCS (ξ ≃ 1000a) limit.