Structural and charge transfer properties of ion intercalated 2D and bulk ice.

Ion trapping at the nanoscale within low-dimensional and bulk ice and their corresponding hydration properties are studied using ab initio techniques. We study the structural and charge transfer properties of ion intercalated two-dimensional (2D) and bulk ice and the corresponding ion hydration properties. We found that (i) the nanochannel size and ionic radius are two important factors that control the spatial distribution of hydrated ions, (ii) the alkali metal and halide ions are located in the center of the graphene-made nanochannel of size ≃6.5 Å, whereas in the nanochannel with size ≃9 Å, large (K+, Rb+, Cl-, Br-, and I-) and small (Li+, Na+, and F-) ions are located in different positions, (iii) the binding energy decreases with increase in the ionic radius, (iv) the hydration of ions decreases for large ions within 2D ice, giving a reduction in coordination number and allowing dehydration of large ions, and (v) the charge transfer mechanism is found to be different for large and small ions.

Single-layer structures of a100- and b010-Gallenene: a tight-binding approach.

Using the simplified linear combination of atomic orbitals (LCAO) method in combination with ab initio calculations, we construct a tight-binding (TB) model for two different crystal structures of monolayer gallium: a100- and b010-Gallenene. The analytical expression for the Hamiltonian and numerical results for the overlap matrix elements between different orbitals of the Ga atoms and for the Slater and Koster (SK) integrals are obtained. We find that the compaction of different structures affects significantly the formation of the orbitals. The results for a100-Gallenene can be very well explained with an orthogonal basis set, while for b010-Gallenene we have to assume a non-orthogonal basis set in order to construct the TB model. Moreover, the transmission properties of nanoribbons of both monolayers oriented along the AC and ZZ directions are also investigated and it is shown that both AC- and ZZ-b010-Gallenene nanoribbons exhibit semiconducting behavior with zero transmission while those of a100-Gallenene nanoribbons are metallic.

The effect of pressure-induced structural transition on exchange interaction function and electronic structure in Gd-element.

In the present work, two models based on the mean field approximation and density functional theory are developed for two independent subsystems - the "local-spin exchange" and "conduction band" - in order to analysis the elimination of exchange anisotropy, where the possibility of Kondo-like behavior in gadolinium-element can be investigated. These models allow us to describe the coupled spin-lattice subsystems in direction to remove the intra-layer loop of exchange of "hexagonal" to lower symmetry of "rhombohedral" (crystallography slip). The intra-layer "a-b" loop exchange, which is the cause of exchange anisotropy, was calculated by the exchange eigenvalue-eigenfunction Jij(R(→) - R(→)') between two completely separate magnetic ions (Rij ≥ 3.6 Š≫ R4f ≈ 0.36 Å) in the metallic Gd-element, where there is no crystal field effect (L = 0) and to a good approximation no notable hybridization in the mean field approximation. In this regard, the pressure induced phase transition of Gd from hexagonal to rhombohedral as the result of the first principle density functional theory by using the Wien2K package within the PBE + U approximation, is investigated. We observed the leakage of d orbitals into f orbitals in the electronic structure of the Gd rhombohedral phase, as well as the coincidence of all three principal directions in the eigenvalue (λmin(K)). Both phenomena can predict the appearance of Kondo-like behavior in Gd.

Temperature dependence of the giant magnetoresistance in Fe/DNA/Fe structure.

A numerical study is presented to investigate the spin-dependent transport through poly(dG)-poly(dC) DNA molecule sandwiched between ferromagnetic contacts in the absence and in the presence of environmental effects. Making use of tight-binding procedure and within the framework of a generalized Green's function technique, the room temperature current-voltage characteristics of DNA molecule and the giant magnetoresistance (GMR) of Electrode/DNA/Electrode structure, with iron (Fe) as the electrode are studied. It is found that the GMR to be lower than 12% for small applied bias and about 35% for applied bias larger than 2.5 volts. Considering the environmental effects, the GMR would be increased up to 13% at a bias lower than 2 volts and decreases up to 23% for the bias about 2.5 volts. In addition, our calculations indicate that for applied biases around 2.5 volts, the GMR decreases when the temperature increased.