Balasaheb J. Nagare

Ferromagnetism in Carbon-Doped Zinc Oxide Systems

We report spin-polarized density functional calculations of ferromagnetic properties for a series of ZnO clusters and ZnO solid containing one or two substitutional carbon impurities. We analyze the eigenvalue spectra, spin densities, molecular orbitals, and induced magnetic moments for ZnC, Zn(2)C, Zn(2)OC, carbon-substituted Zn(n)O(n) (n = 3-10, 12) clusters and the bulk ZnO. The results show that the doping induces magnetic moment of approximately 2 mu(B) in all the cases. All systems with two carbon impurities show ferromagnetic interaction, except when carbon atoms share the same zinc atom as the nearest neighbor. This ferromagnetic interaction is predominantly mediated via pi-bonds in the ring structures and through pi- and sigma-bonds in the three-dimensional structure. The calculations also show that the interaction is significantly enhanced in the solid, bringing out the role of dimensionality of the Zn-O network connecting two carbon atoms.

Electronic structure of the spin gapless material Co-doped PbPdO2

First-principles electronic structure calculations are performed for the pure and Co-doped PbPdO2 using plane wave density functional method using different exchange-correlation functionals. These calculations indicate the 25% Co-doped PbPdO2 to be a spin gapless semiconductor, as proposed earlier [X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008)]. Insights into the nature of magnetic interaction between the Co-spins and its origin are developed through calculations over a wide range of Co concentrations.

Interaction of O 2 , CO 2 , NO 2 and SO 2 on Si- doped Carbon Nanotube

We report reactivity of silicon doped single walled carbon nanotube (Si-CNT) towards the small atmospheric gas molecules O 2 , CO 2 , SO 2 and NO 2 using density functional theory based on the numerical basis set method. The reactivity of gas molecules is explained with binding energy, band structure, charge density, and density of states. We found that the substitutional doping of silicon atom in CNT increases the binding energy as compared with pure CNT. The charge density analysis reveals the formation of sigma (σ) bonds between silicon and carbon atoms. Further, the band structure and density of states clearly illustrate the creation of extra state near the Fermi level and reduction in the band gap, which acts as a reactive center for adsorption of the molecules on Si-CNT. We have observed that the large value of adsorption energy shows the chemisorption between molecules and Si-CNT. Mulliken population analysis clearly reveals the charge-induced dipole interactions between the Si-CNT and molecules, which are responsible for chemisorption for gas molecules. The donor like impurity state generated in energy gap almost disappears after adsorption of all gas molecules excluding NO 2 . We further note that molecules accept the electronic charge from nanotubes and have significant influence on electronic structure near the Fermi level and are responsible for the increase in the p-type conductivity of tubes.

Hydrogen adsorption on Na–SWCNT systems

We investigate the hydrogen adsorption capacity of Na-coated carbon nanotubes (Na-SWCNTs) using first-principles electronic structure calculations at absolute temperature and pressure. A single Na atom is always found to occupy the hollow site of a hexagonal carbon ring in all the six different SWCNTs considered, with a nearly uniform Na–C bond length of 2.5 A. Semiconducting zigzag nanotubes, (8,0) and (5,0), show stronger binding energies for the Na atom (−2.1 eV and −2.6 eV respectively), as compared to metallic SWCNTs with armchair and chiral geometries. The single Na atom can further adsorb up to six hydrogen molecules with a relatively constant binding energy of −0.26 eV per H2. Mulliken population analysis shows that positively charged Na atoms with 0.82e charge transfer to nearest carbon atoms which polarizes the SWCNT leading to local dipole moments. This charge-induced dipole interaction is responsible for the higher hydrogen uptake of Na-coated SWCNTs. The transition state search shows that the diffusion barrier of Na atom on the SWCNT between two adjoining C–C rings is 0.35 eV. We also investigate the clustering of Na atoms to find out the maximum weight percentage adsorption of H2 molecules. At high Na coverage, we show that Na-coated SWCNTs can adsorb 9.2–11.28 wt% hydrogen. Our analysis shows that, although indeed Na-coated SWCNTs present potential materials for the hydrogen storage, care should be taken to avoid Na atoms clustering on the support material at elevated temperature and pressure, to achieve higher hydrogen capacity.

First-Principle Study of Hydrogen Adsorption on Na-Coated Carbon Nanotubes

We investigate the hydrogen adsorption capacity of Na-coated carbon nanotube using first-principles plane wave method. A single Na atom always occupies the hollow site of a hexagonal carbon ring in all, with a nearly uniform Na-C bond length of 2.5 A. Semiconducting zigzag nanotubes, (8,0) show stronger binding energies of the Na atom of -2.1 eV. The single Na atom can further adsorb up to six hydrogen molecules with a relatively constant binding energy of -0.26 eV/H2. Mulliken population analysis shows that positively charged Na atoms with 0.82e charge transfer to nearest carbon atoms which polarizes the CNT leading to local dipole moments. This chargeinduced dipole interaction is responsible for the higher hydrogen uptake of Na-coated CNT. We also investigate the clustering of Na atoms to find out the maximum weight percentage adsorption of H2 molecules. At high Na coverage, we show that Na-coated CNTs can adsorb 9.2 wt % hydrogen. Our analysis shows that, although indeed Na-coated CNT present potential material for the hydrogen storage, care should be taken to avoid Na atoms clustering on support material, to achieve higher hydrogen

The optical response of nanoclusters under confinement

We report the optical properties of metallic and semiconductor nanoclusters with various sizes as a function of confinement using real-space time dependent density functional theory (TDDFT). The lowest equilibrium structures have been selected by examining the evolution of the lowest five isomers for each cluster as a function of volume for six different compressions. The minimum volume considered is about 1/10th of the free space box volume. The absorption spectra depict a blue shift, an increase in intensity and a change in line shape of the spectral lines of the confined systems. The observed enhancement in the intensity of the spectral lines is found to be about two- to three-fold at high compression compared to their counterparts. This is accompanied by an increase in the optical band gap and excitation energy of the transitions with compression. In all of the systems that we investigate, the observed blue shift, an enhanced intensity and a change in line shape of the spectral lines are found to be generic in nature.

Comparative study of adsorption of O 2, CO 2, NO 2 and SO 2 on pristine and Si-Doped Carbon Nanotubes

Density functional theory is used to investigate the adsorption properties of O2, CO2, SO2 and NO2 gas molecules on pristine carbon nanotube (CNT) and Si-doped carbon nanotube (Si-CNT). All molecules except NO2 are physisorbed, with essentially no charge transfer between the CNT and molecules. The electronic properties of CNT are sensitive to the adsorption of NO2 because of its chemisorption, while they are insensitive to the O2, CO2 and SO2 molecules. The weak binding of these molecules on CNT is due to formation of charge-dipole interactions. In case of Si-CNT, all molecules are chemisorbed to the Si-C bonds with appreciable adsorption energy and significant charge transfer. The density of state analysis shows that the additional state near the Fermi level due to doping of silicon is responsible for chemisorption of the molecules. Further, our theoretical results suggest that molecule-induced modification of the density of states close to the Fermi level might significantly affect the transport properties of nanotubes.

Optical properties of alkali substituted boron clusters using TDDFT method

The alkali substituted boron (Bn and Bn−1X with n = 2 – 4, X = Li, Na and K), have been theoretically investigated using time dependent density functional theory calculations. The geometric structures and optical properties of these clusters are systematically analyzed. The impact of doping alkali atom on replacing one boron from Bn clusters are studied for binding energy per atom, ionization potential, electron affinity and optical gap. The optical spectra have been examined for pure and alkali doped boron. The absorption spectra formed by quite smooth peaks. The main effect of alkali doping is that wider energy range distribution with a significant reduction of the oscillator strength comparative to the pure clusters.The alkali substituted boron (Bn and Bn−1X with n = 2 – 4, X = Li, Na and K), have been theoretically investigated using time dependent density functional theory calculations. The geometric structures and optical properties of these clusters are systematically analyzed. The impact of doping alkali atom on replacing one boron from Bn clusters are studied for binding energy per atom, ionization potential, electron affinity and optical gap. The optical spectra have been examined for pure and alkali doped boron. The absorption spectra formed by quite smooth peaks. The main effect of alkali doping is that wider energy range distribution with a significant reduction of the oscillator strength comparative to the pure clusters.