The geometric and electronic structures of Eu doped single-walled carbon nanotubes (SWCNTs) have been studied using density functional theory. Three different doping configurations are considered. All of these configurations are stable upon relaxation, and Eu atom on the top of the inside hole site is the most favorable configuration for most nanotubes, except (3,3) CNT. The formation energies vary regularly with the same trend as in the Co and Fe doped cases. The electronic structures studies indicate that the charge transfer basically occurs between 5d6s of Eu and the antibonding orbital of the C6 ring of the SWCNT. Eu atom is monovalent for the exohedral and substitutional doping, and for the endohedral doping of large radius nanotubes; it is bivalent for endohedral doping of (3,3) tube. As the radius increases, the net charges on Eu atom steadily decrease for exohedral and endohedral doping. The magnetic moments of Eu atoms are preserved in all of the configurations, but they vary with the radius of nanotube and adsorbing sites. 相似文献
Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of ?0.1?eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms which are bound to the nickel. The adsorption energy of ?1.4?eV and zero activation energy barrier indicate that O2 dissociative adsorption is both thermodynamically and kinetically favoured over the surface. The large electric field near the doping nickel atom along with the excess electrons on the neighbouring carbon atoms, which are bound to the nickel induce molecular oxygen to adsorb and dissociate favourably. 相似文献
The electronic structures and magnetic properties in zinc-blende structure ZnS doped with nonmagnetic noble metal palladium have been investigated by means of density functional theory (DFT) calculations employing the generalised gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U). Both the GGA and GGA + U methods demonstrate half-metallicity in Pd-doped ZnS with total magnetic moments of about 2.0μB per supercell. The half-metallic ferromagnetism stems from the hybridisation between Pd-4d and S-3p states and could be attributed to a double-exchange mechanism. These results suggest a recipe for obtaining a promising dilute magnetic semiconductor by doping nonmagnetic 4d elements in ZnS matrix. 相似文献
The adsorption and reaction behaviors of CF3CH2I on Ag(111) were systematically studied by density functional theory (DFT) calculations. Physical adsorption of CF3CH2I on Ag(111) occurs due to the weak interactions between surface Ag atoms and iodine atom of CF3CH2I; while strong chemisorption occurs for CF3CH2 fragment on Ag(111). Electronic analysis indicates that the singly occupied molecular orbital (SOMO) of CF3CH2 strongly interacts with the surface Ag atoms. It is very interesting to find that the most stable structures of CF3CH2 on Ag(111) locate at the top site, instead of the hollow sites. This might be attributed to the facts that CF3CH2 adsorbed at the top site will maximize the sp3-type hybridization, and the possible weak interaction between the fluorine lone pair electrons of p orbitals for CF3CH2 and surface Ag(111) occurs, which is supported by the charge density difference (CDD) analysis with a low isosurface value. We propose that the charge density difference (CDD) analysis with a high or low isosurface value can be widely applied to analyze the strong or weak electronic interactions upon adsorption. Transition state calculations suggested that the energy barrier of CF bond rupture for CF3CH2I on Ag(111) (1.44 eV) is much higher than that of CI bond breakage for CF3CH2I (0.43 eV); and the activation energy of the CF bond dissociation for CF3CH2(a) is 0.67 eV. 相似文献
The main objective of this study is to understand the sensing origin of anatase TiO2 and provide an insight into why gas sensitivity of anatase TiO2 is not so excellent.
