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Minuscule molecular forces can transform DNA into a structure that is elongated by more than half its original length. We demonstrate that this pronounced conformational transition is of relevance to ongoing experimental and theoretical efforts to characterize the conducting properties of DNA wires. We present quantum mechanical calculations for acidic, dry, poly(CG).poly(CG) DNA which has undergone elongation of up to 90 % relative to its natural length, along with a method for visualizing the effects of stretching on the electronic eigenstates. We find that overstretching leads to a drastic drop of the hopping matrix elements between localized occupied electronic states suggesting a dramatic decrease in the conductivity through holes.
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Topological aspects of the geometry of DNA and similar chiral molecules have received a lot of attention, while the topology of their electronic structure is less explored. Previous experiments have revealed that DNA can efficiently filter spin-polarized electrons between metal contacts, a process called chiral-induced spin-selectivity (CISS). However, the underlying correlation between chiral structure and electronic spin remains elusive. In this work, we reveal an orbital texture in the band structure, a topological characteristic induced by the chirality. We find that this orbital texture enables the chiral molecule to polarize the quantum orbital. This orbital polarization effect (OPE) induces spin polarization assisted by the spin-orbit interaction from a metal contact and leads to magnetorestistance and chiral separation. The orbital angular momentum of photoelectrons also plays an essential role in related photoemission experiments. Beyond CISS, we predict that OPE can induce spin-selective phenomena even in achiral but inversion-breaking materials.
We study the electronic structure of graphene in the presence of either sevenfolds or eightfolds by using a gauge field-theory model. The graphene sheet with topological defects is considered as a negative cone surface with infinite Gaussian curvature at the center. The density of electronic states is calculated for a single seven- and eightfold as well as for a pair of sevenfolds with different morphology. The density of states at the Fermi energy is found to be zero in all cases except two sevenfolds with translational factor $M eq 0$.
We apply first-principles calculations to study the electronic structure of boron nitride nanocones with disclinations of different angles $theta=npi/3$. Nanocones with odd values of $n$ present antiphase boundaries that cause a reduction of the work function of the nanocones, relative to the bulk BN value, by as much as 2 eV. In contrast, nanocones with even values of $n$ do not have such defects and present work functions that are very similar to the BN bulk value. These results should have strong consequences for the field emission properties of boron nitride nanocones and nanotubes.
We address the low-energy effective Hamiltonian of electron doped d0 perovskite semiconductors in cubic and tetragonal phases using the k*p method. The Hamiltonian depends on the spin-orbit interaction strength, on the temperature-dependent tetragonal distortion, and on a set of effective-mass parameters whose number is determined by the symmetry of the crystal. We explain how these parameters can be extracted from angle resolved photo-emission, Raman spectroscopy, and magneto-transport measurements and estimate their values in SrTiO3.
New theoretical and experimental investigation of the occupied and unoccupied local electronic density of states (DOS) are reported for alpha-Li3N. Band structure and density functional theory calculations confirm the absence of covalent bonding character. However, real-space full-multiple-scattering (RSFMS) calculations of the occupied local DOS finds less extreme nominal valences than have previously been proposed. Nonresonant inelastic x-ray scattering (NRIXS), RSFMS calculations, and calculations based on the Bethe-Salpeter equation are used to characterize the unoccupied electronic final states local to both the Li and N sites. There is good agreement between experiment and theory. Throughout the Li 1s near-edge region, both experiment and theory find strong similarities in the s- and p-type components of the unoccupied local final density of states projected onto an orbital angular momentum basis (l-DOS). An unexpected, significant correspondence exists between the near-edge spectra for the Li 1s and N 1s initial states. We argue that both spectra are sampling essentially the same final density of states due to the combination of long core-hole lifetimes, long photoelectron lifetimes, and the fact that orbital angular momentum is the same for all relevant initial states. Such considerations may be generically applicable for low atomic number compounds.
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