Narrow Results

In this paper, we study the electrical transport and Negative Differential Resistance (NDR) in a single molecular conductor consisting of a cysteine sandwiched between two Au(111) electrodes via the Density Functional Theory-based Nonequilibrium Green's Function (DFT-NEGF) method. We show that (surprisingly, despite their apparent simplicity, these Au/cysteine/Au nanowires are shown to be a convenient NDR device) the smallest two-terminal molecular wire can exhibit NDR behavior to date. Experiments with a conventional or novel self-assembled monolayer (SAM) are proposed to test these predictions.

The projected density of states (PDOSs) and transmission coefficients T(E) under various external voltage biases are analyzed, and it suggests that the variation of the coupling between the molecule and the electrodes with external bias leads to NDR.

We investigated the stability of aminoborane with electron withdrawing groups such as –CF₃ and –CN using density functional theory calculations. For the electron withdrawing groups of –CF₃ and –CN, we observed similar tendency of B–N bond strength: electron withdrawal from the N atom reduces the strength of B–N bonds. And we find that the electron density localized on B and N is also reduced through the charge analysis. These electron withdrawing substituents make cyclic dimers and trimers stabilized less than electron donating ones.

In the present work, we have investigated solvent effects on the relative energies and dipole moment values and studied the structural properties of water, methanol, and ethanol surrounding single-walled carbon nanotube (SWCNT) and mixtures of them as well, using Molecular Dynamics simulation. Because some of the physicochemical parameters are related to structural properties of SWCNT, we used different force fields to determine energy and other types of geometrical parameters, on the particular SWCNT. Because of the differences among force fields, the energy of a molecule calculated using two different force fields will not be the same. In this study, the difference in the force fields is illustrated by comparing the calculated energies by using force fields such as MM+, AMBER, and BIO+. The Quantum Mechanics (QM) calculations were carried out with the GAUSSIAN 98 program based on HF/3-21G level. In this study, we have compared gas phase and solvent calculations that considered solvents such as water, methanol, ethanol, and mixtures of them. So, in this work, we investigated polar solvents effects on SWCNT within the Onsager self-consistent reaction field (SCRF) model using a Hartree–Fock method and the temperature effect on the stability of SWCNT in various solvents.

A systematic study of structural, electronic and vibrational properties of boron- and nitrogen-doped heterofullerenes has been performed. N and B doping lead to the structural deformation, and the dopant has a tendency to occupy a single position in a pentagon and two positions in a hexagon which are not adjacent. B-substitution produces clusters of greater thermodynamic stability than N substitution. The C–N and C–B bond lengths lie in the range of 1.40–1.44 Å and 1.53–1.57 Å for hexagon–hexagon (6, 6) and 1.39–1.46 Å and 1.55–1.60 Å at pentagon–hexagon (5, 6) interfaces, respectively. The Mulliken charge analysis shows a charge transfer of -0.30 to -0.45 electrons from N to C atoms; B atom act as electron acceptors with charge gain ranging between -0.59 to -0.70 electrons. N- and B-doping in fullerene molecules present an interesting way to alter electronic and chemical properties of the _C60 molecule for useful device applications.

Zinc oxide (ZnO) electrical properties can be modified by addition of impurities or defects such as vacancies or other substances. We use sulfur (S) as a substitutional impurity and present a theoretical study on the characteristics of ZnO structures in its crystal form containing S in substitution of O. For theoretical calculations we used Density Functional Theory (DFT) with pseudopotentials and plane waves. ZnO in crystal form with S in substitution of O at heavy percentage was studied by analyzing properties like lattice characteristics, total energy, and gap energy. Lattice parameters a, b, c, and c/a ratio increase with the S-substituent percentage while the crystal stability decreases. Variation of gap energy shows a decreasing trend with increasing amount of substitution. In this paper, we provide a detailed data useful to identify the effects on ZnO in its crystal form when O is replaced by S that will help to predict if the structural changes on the modified ZnO structures may be suitable for applications in opto-electronics.

We present a first principle calculation on the electronic structure and the linear optical properties of (13-0) zigzag single walled carbon nanotube by using full potential linear augmented plane wave (FP-LAPW) method. It is found that zigzag (13-0) nanotube has semiconducting behavior with the band gap of 0.6 eV at Γ point. The optical spectra of (13-0) carbon nanotube have been calculated for both electric field polarizations, parallel and perpendicular to the tube axis. The dielectric function is found to be highly anisotropic and is much larger for the electric field applied along the tube axis than the perpendicular. The results show that unlike the optical absorption, the energy loss function of (13,0) SWCNT show weak anisotropy. It was also revealed that the energy loss function peaks for both electric fields happen almost at the same energies, but with rather difference in their amplitudes.

The electronic and magnetic properties of Fe atomic wire and atomic plane have been theoretically investigated from full potential linearized augmented plane wave (FPLAPW) method within a frame work of density functional theory (DFT). This work is based on the comparative study of number of Fe nanochains with infinite length and infinitely spread Fe nanosheet. A most commonly adopted GGA approximation is used for electron exchange correlation. In our calculation, the property of Fe-chain is predicted to be magnetic metal with the presence of deep valley (in Spin-up DOS) and a peak (in Spin-down DOS) at Fermi level ($E_F$) shows the antisymmetric DOS. The presence of antisymmetric DOS is a signature of exchange splitting between the degenerated d-states. The splitting between t${}_{2g}$ states is very prominent in Fe-chain which enhances the magnetic moment. The magnetic moment decreases with the increase in number of Fe-chains.

The stabilities and reactivities of two transition metal ($X=\mathrm{\text{Cu}}$, Zn)-doped structures of C${}_{20}$ fullerene have been investigated by density functional theory approach. We have observed a noticeable structural change in pristine C${}_{20}$ due to the substitution of one of its carbon atom by Cu or Zn atom. From our findings, it is found that the energy gap of C${}_{19}$Cu and C${}_{19}$Zn increases with respect to pristine C${}_{20}$, thus making the two doped fullerenes more stable than their pristine counterpart. The reactivity parameters such as chemical hardness, chemical potential and electrophilicity index for these structures are also studied. Interestingly, our calculations reveal that both the doped fullerenes obey the maximum hardness principle and minimum electrophilicity principle. Also, from the electronic absorption spectra analysis, it can be inferred that the maximum absorption peak of the two heteroatom-substituted fullerenes C${}_{19}$Cu and C${}_{19}$Zn are shifted towards the longer wavelength region as compared to the pure C${}_{20}$ fullerene, which clearly indicates that a red shift is introduced on account of doping.

The effects of relative positions of Se atoms in a monomolecular layer of MoS${}_{1.5}$Se${}_{0.5}$ have been studied. It is demonstrated that the distribution of Se atoms between top and bottom chalcogen planes is most energetically favorable. For a more probable distribution of Se atoms this monolayer alloy is a direct semiconductor with the fundamental bandgap of 2.35eV. We have also evaluated the optical band gaps of the alloy at 77K (1.86eV) and room temperature (1.80eV), which are in a good agreement with the experimentally measured bandgap of 1.79eV.

Isobaric heat capacities of C${}_{60}$(OH)${}_{40}$ and C${}_{70}$(OH)${}_{12}$ fullerenols were measured using adiabatic calorimetry in the temperature range of 0–320K along with standard thermodynamic functions: $S_m$, [${\mathrm{\Phi }}_m(T)-{\mathrm{\Phi }}_m(0)$] and [$H_m(T)-H_m(0)$]. Furthermore, the molar entropy of formation and the molar third law entropy of C${}_{60}$(OH)${}_{40}$ and C${}_{70}$(OH)${}_{12}$ in crystalline state at 298.15K were calculated.

The impact of hydrogen on the conductivity and vibration for zinc oxide (ZnO) nanoparticles had implicated for nanoscale optoelectronic units. Infrared reflectance spectra for ZnO hydrogen-annealed nanoparticles were calculated at incidence. The theory of density functional theory is applied to the reflectance model and absorption spectra. There is an agreement between both the model suggesting that the nanoparticles have inhomogeneous carriers’ concentrations and the experimental results. A significant decrease in carrier concentration resulted from exposure to oxygen for several hours, according to the adsorption on the nanoparticle surface of negative oxygen molecules. Also, the density of states in deferent wurtzoid’s size has been studied. The experimental energy gap values of bulk ZnO, HOMO and LUMO levels as a function of the total Zn and O atoms number in ZnOH diamondoids were determined, as well as the bond length in deferent wurtzoid’s size where the experimental ZnO bond length at 1.9767 Å has been calculated. The tetrahedral angles in deferent wurtzoid’s size were studied, deferent wurtzoid’s size Reduced mass as a vibration frequency function and force constant as a function of vibrational frequency in deferent wurtzoid’s size were determined. A good result for infrared as a vibration frequency function in deferent wurtzoid’s size has been found, as well as Raman as a vibration frequency function in deferent wurtzoid’s size.

In this study, the electronic and magnetic properties of hydrogen-passivated armchair and zigzag GaN nanoribbons are investigated using density-functional theory. We explore that doped TM atom leads to additional levels in the band gap and thus plays an essential role in spin polarization and changes their properties. Depending on its location in the nanoribbon, the character of spin-dependent electronic property of a doped GaN-NR was analyzed. Our calculations show that, regardless of the position of Mn atoms, GaNNTs are stable in ferromagnetic phase.