Papers by Keyword: Density Function Theory (DFT)

Abstract: By using spin polarized density functional calculations, we investigate the effect of oxygen molecule adsorption on the structural and electrical properties of (8, 0) single wall carbon nanotube. The obtained results indicate endothermic chemisorption of O₂ on the nanotube surface with a large binding energy of about 598 meV and a significant charge transfer of about 0.43 e^- per molecule. We find that despite the triplet ground state configuration of free oxygen molecule, adsorbed oxygen on the nanotube prefers a zero moment spin singlet state. It is discussed that O₂ chemisorption dopes the (8, 0) carbon nanotube with hole carries and thus increases its work function from 4.34 to 4.89eV. This hole doping effect may show potential applications of carbon nanotubes in conductivity and thermopower electric based sensors.

Abstract: A series of chiral [6]helicenes have been designed using the molecular engineering of organic nonlinear optical materials. The geometries of [6]helicenes 1, 2, 3, 4,5 are optimized using density functional theory (DFT-B3LYP) method at the 6-31g (d, p) basis set level. Based on the obtained stable molecular configuration, we adopt the TDHT/PM3 method and time-dependent density-functional theory (TD-DFT) to calculate the nonlinear optical (NLO) properties and electronic spectra of these molecules. Results show that the static hyperpolarizability βµ alternates between positive value and negative value, whereas it remains positive for the molecues 2 and 3 which have medium magnitudes βµ, 3.4×10-30esu and 9.6×10-30esu respectively. In molecule 5, there exists two competitive charge transfers that reduce the hyperpolarizability β.

Abstract: By using the density functional theory (DFT), we have investigated CO molecules adsorbed on palladium atom doped (Pd-doped) (5, 5) and (6, 6) boron nitride nanotubes (BNNTs). In order to investigate the electronic and structural properties of all the research objects, we calculated the band gap (Eg), bind energy (Eb), and density of state (DOS). The results show that energy gaps of BNNTs reduced by doped impurity Pd atom, but there are no obvious changes with the tube diameter of Pd-BNNTs change. One impurity Pd atom substituting one B (PdB) or N atom (PdN) of pristine BNNTs can increase the reactivity with CO molecule. The energy gaps for CO molecule adsorption on the tube wall of Pd-BNNTs reduced. This indicates that Pd-doped BNNTs can be considered as nano gas sensitive material.

Abstract: Using first principles density functional theoretical calculations within the generalized gradient approximation (GGA), the present paper reports thermal properties such as constant volume lattice specific heat, Gibbs free energy, internal energy, and entropy of Yb-pnictides such as YbN, YbP and YbAs in its rocksalt phase. The variation of lattice specific heat with temperature obeys the classical Dulong-Petits law at high temperature while at low temperature it obeys Debye T³ law. The internal energy, entropy and free energy show a gradual variation with temperature. The specific heat at constant volume at lower temperature increases as going from N to P to As. ^*Corresponding author Email: pkj@bhavuni.edu, prafullaj@yahoo.com Telephone: +91-278-2422650 Fax: +91-278-2426706

Abstract: The structural, electronic, optical and elastic properties of zinc-blende compounds (CdX, X = S, Se and Te), were studied using full-potential augmented plane wave plus local orbitals method (FP-LAPW+ lo) within density functional theory, using generalized gradient approximation (GGA). Geometrical optimization of the unit cell (lattice constant, bulk modulus and its pressure derivative) is in good agreement with experimental data. Results for band structures, density of states, and elastic constants (C₁₁, C₁₂ and C₄₄) are presented. We also report our results on optical properties like the complex dielectric functions and the refractive index (n) of these compounds. Our results are in reasonable agreement with the available theoretical and experimental data.

Abstract: A systematic theoretical study of 4d transition metal nitride, PdN has been carried out using ab initio full potential LAPW method (FP-LAPW) within the generalized gradient approximation (GGA). PdN crystallizes in zinc-blende structure, which is found to be most stable one. We have calculated the ground state properties in terms of lattice constant (a₀), Bulk modulus (B₀) and its Pressure derivative (B₀). The electronic properties such as band structure and density of states reveal that PdN is metallic in nature with large overlap of Pd-d electron at Fermi level. The elastic constant are in good agreement with previous theoretical results for zinc-blende structure.

Abstract: We demonstrate that the formation of carbonate-like moiety in SiO₂ could be the origin of negative fixed charge in SiC thermal wet oxidation, based on first-principles calculations. We find that negative CO₃ ion appears in SiO₂ due to not only the existence of residual C atoms that are expected to be emitted from the SiC/SiO₂ interface, but also a large enough number of incorporated H atoms during wet oxidation.

Abstract: Molecule-sized fluorescent emitters are much sought-after to probe biomolecules in living cells. We demonstrate here by time-dependent density functional calculations that the experimentally achievable 1-2 nm sized silicon carbide nanocrystals can emit light in the nearinfrared region after introducing appropriate color centers in them. These near-infrared luminescent silicon carbide nanocrystals may act as ideal fluorophores for in vivo bioimaging.

Abstract: Using first-principles calculations, we investigated the migration mechanisms of Cl in cubic SiC. The analysis of the formation energies of several defect configurations (isolated interstitials and complex defects), either reported in the literature or calculated in the present study, revealed that three migration mechanisms are possible: Interstitialcy and two different vacancy-mediated mechanisms (both concerted exchange and second-neighbor hop). Our calculations showed that vacancy-mediated diffusion is more energetically favorable than an intersticialcy one and the values of the diffusivity, for both n-type and p-type SiC were also estimated.

Abstract: We have studied the structures and electronic properties of PdCn (n=2-12) using the density functional theory in this paper. Though calculating, we found that the linear isomers are most stable for PdCn(n=2-9) clusters. N=10 is turning point, and the bicyclical structure is most stable for PdC10 cluster. Cyclic structures have the lowest energy for PdC11 and PdC12 clusters.