Tuneable molecular doping of corrugated graphene

Density functional theory (DFT) modeling of the physisorption of four different types of molecules (toluene, bromine dimmer, water and nitrogen dioxide) over and above graphene ripples has been performed. For all types of molecules changes of charge transfer and binding energies in respect to flat graphene is found. The changes in electronic structure of corrugated graphene and turn of {\pi}-orbitals of carbon atoms in combination with chemical structure of adsorbed molecules are proposed as the causes of difference with the perfect graphene case and variety of adsorption properties of different types of the molecules. Results of calculation suggest that the tops of the ripples are more attractive for large molecules and valley between ripples for small molecules. Stability of molecules on the ripples and energy barriers for migration over flat and corrugated graphene is also discussed.Comment: 15 pages, 5 figures, accepted in Surface Scienc

Mn clusterisation in Ga1-xMnxN

Local structure of Mn atoms in Ga1-xMnxN has been investigated by the Mn L3 edge x-ray absorption spectrum (XAS) at total electron yield mode, which preferentially looks at atoms near the surface. A modeling defects configuration, the Mn5 micro-clusters complexed with substitutional MnGa and interstitial MnI is found for the higher Mn doping concentration. This new configuration is also confirmed by the total energy calculations.Comment: 17 pages, 5 figures, to be published in Solid. State Commu

DFT calculation of the intermolecular exchange interaction in the magnetic Mn4_4 dimer

The dimeric form of the single-molecule magnet [Mn$_4$O$_3$Cl$_4$(O$_2$CEt)$_3$(py)$_3$]$_2$ recently revealed interesting phenomena: no quantum tunneling at zero field and tunneling before magnetic field reversal. This is attributed to substantial antiferromagnetic exchange interaction between different monomers. The intermolecular exchange interaction, electronic structure and magnetic properties of this molecular magnet are calculated using density-functional theory within generalized-gradient approximation. Calculations are in good agreement with experiment.Comment: 4 page

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques - X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ~21 nm in size plus a cubic phase admixture of only 2 at. % composed of primary edge-boundary nanoparticles ~15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd...O-OH] and [Gd...O-O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5p - O 2s core-like levels in the valence band structures. The origin of [Gd...O-OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT-van der Laan model, and good agreement was established.Comment: 27 pages, 10 figures, accepted in Appl. Surf. Sc

Nuclear spin-lattice relaxation in ferrimagnetic clusters and chains: A contrast between zero and one dimensions

Motivated by ferrimagnetic oligonuclear and chain compounds synthesized by Caneschi et al., both of which consist of alternating manganese(II) ions and nitronyl-nitroxide radicals, we calculate the nuclear spin-lattice relaxation rate 1/T_1 employing a recently developed modified spin-wave theory. 1/T_1 as a function of temperature drastically varies with the location of probe nuclei in both clusters and chains, though the relaxation time scale is much larger in zero dimension than in one dimension. 1/T_1 as a function of an applied field in long chains forms a striking contrast to that in finite clusters, diverging with decreasing field like inverse square root at low temperatures and logarithmically at high temperatures.Comment: to be published in Phys. Rev. B 68 August 01 (2003

Electronic structure of a Mn12 molecular magnet: Theory and experiment

金沢大学大学院自然科学研究科物質情報解析We used site-selective and element-specific resonant inelastic x-ray scattering (RIXS) to study the electronic structure and the electron interaction effects in the molecular magnet [Mn12 O12 (C H3 COO)16 (H2 O)4] 2C H3 COOH 4 H2 O, and compared the experimental data with the results of local spin density approximation +U electron structure calculations which include the on-site Coulomb interactions. We found a good agreement between theory and experiment for the Coulomb repulsion parameter U=4 eV. In particular, the p-d band separation of 1.8 eV has been found from the RIXS spectra, which is in accordance with the calculations. Similarly, the positions of the peaks in the XPS spectra agree with the calculated densities of p and d states. Using the results of the electronic structure calculations, we determined the intramolecular exchange parameters, and used them for diagonalization of the Mn12 spin Hamiltonian. The calculated exchanges gave the correct ground state with the total spin S=10. © 2007 The American Physical Society

Tuning the gap in bilayer graphene using chemical functionalization: DensityFunctional (DFT) calculations

Contains fulltext : 72410.pdf (preprint version ) (Open Access)5 p

Hydrogen storage on graphene: First-principle calculations

Contains fulltext : 34643.pdf (preprint version ) (Closed access)Density functional calculations of electronic structure, total energy, structural distortions, and magnetism for hydrogenated single-layer, bilayer, and multi-layer graphene are performed. It is found that hydrogen-induced magnetism can survives only at very low concentrations of hydrogen (single-atom regime) whereas hydrogen pairs with optimized structure are usually nonmagnetic. Chemisorption energy as a function of hydrogen concentration is calculated, as well as energy barriers for hydrogen binding and release. The results confirm that graphene can be perspective material for hydrogen storage. Difference between hydrogenation of graphene, nanotubes, and bulk graphite is discussed.1971 p

Electronic structure and exchange interactions in V-15 magnetic molecules: LDA+U results

Contains fulltext : 60385.pdf (publisher's version ) (Open Access)Single-molecule magnets of the type V-15(K-6[V15As6O42(H2O)].8H(2)O) have attracted a great deal of attention recently, being promising systems for studying low-temperature spin-relaxation and quantum-spin tunneling. To understand in detail the internal magnetic and electronic structure, and the intramolecular interactions responsible for the formation and low-energy excitations in V-15 molecules, we have performed electronic structure calculations using the LSDA+U approach. The calculated values of magnetic moments and charge states of vanadium ions agree well with experiments, thus confirming the V4+ state of vanadium ions with a well-defined spin 1/2. We found that the account of the on-site Coulomb repulsion is important for correct description of V-15 internal properties; in particular, for the values of the on-site repulsion parameter Usimilar to4-5 eV, we can achieve good agreement with known properties of V-15, such as the temperature dependence of susceptibility, and the energies of the low-lying eigenstates of the spin Hamiltonian