Search results for "FUNCTIONAL"
showing 10 items of 4822 documents
Hybrid functional calculations on the Na and K impurities in substitutional and interstitial positions in Cu2ZnSnSe4
2015
We studied the energetics, atomic and electronic structure of Na and K extrinsic defects in Cu2ZnSnSe4 by ab initio calculations using the HSE06 hybrid functional. Our results show that (i) among all substitutional positions, the Cu-site is the most favorable position for both Na and K. (ii) The tetrahedrally coordinated interstitial site has a lower formation energy than the octahedrally coordinated interstitial site. (iii) Based on the band structure calculations we can conclude, Se-related defects lead to the formation of defect states within the band gap.
Anomalous binding sequence of CO ligands to an anionic triplatinum carbonyl complex
2005
Abstract A systematic density functional theory study on the structures and binding energies of triplatinum carbonyls Pt 3 ( CO ) x q , with x = 1–6 and q = 0, −1, reveals an anomalous trend in binding energies of the CO ligands to the triangular platinum core, with the first three ligands strongly bound at terminal Pt sites, followed by weaker bound ligands at Pt–Pt bridge sites for x = 4–6. This work provides a novel explanation to the anomalous CO binding trend reported in mid-1990s from collision-induced dissociation and photodissociation experiments.
Phase competition in (La1 − c,Src)CoO3solid solutions:ab initiothermodynamic study
2013
Statistical thermodynamics and density functional theory (DFT) formalisms are combined to analyze the phase competition of energetically preferable phases in (La1 − c,Src)CoO3 solid solutions upon LaCoO3 doping with Sr. La/Sr sublattice in ABO3 perovskite structure is considered as immersed in the field of CoO3 units and the superstructures that are stable with respect to the formation of antiphase domains are analyzed. The concentration-dependent energy parameters determining the relative stability of the cubic superstructures (phases) are extracted. This allows us calculations of concentration- and temperature dependences of the long-range order (LRO) parameters for different phases. The …
Ab initio calculation of wurtzite‐type GaN nanowires
2007
Ab initio calculations of wurtzite-type GaN nanowires have been performed using density functional theory. Different shapes of nanowires of with similar diameters of around 2 nm have been considered to determine the stability of the structures. The quantitative similarities in the local properties obtained and dangling bond energies of nanowires and bulk surfaces have lead to a simple model model for a calculation of effective Young's modulus of nanowires of arbitrary diameters and shapes. The size dependence of the Young's modulus reveals a softening of GaN nanowires with the decrease of the diameter. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical study of Zn and Cd interstitials and substitutional interstitials in CuInSe2 via hybrid functional calculations
2013
We have investigated the formation of Zn and Cd interstitials in the CuInSe2 solar cell material via density-functional-theory (DFT) calculations by employing the HSE06 hybrid functional. The computed formation energies for Zn interstitials were in the range of 2.09-2.68 e V, and in the range of 2.04-2.25 eV for substitutional interstitials. In constrast, the formation energies of Cd interstitials and substitutional interstitials were between 1.85-2.75 eV and 2.41-2.64 eV, respectively. Thus, these results indicate, that Cd interstitials are more likely to be formed than Zn interstitials, and that in case of Zn inclusion into CuInSe2 Zn atoms will prefer to adopt substitutional interstitial…
Ab initiosimulations on rutile-based titania nanowires
2012
The rod symmetry groups for monoperiodic (1D) nanostructures have been applied for construction of models for bulk-like TiO2 nanowires (NWs) cut from a rutile-based 3D crystal along the chosen [001] and [110] directions of crystallographic axes. In this study, we have considered nanowires described by both the Ti-atom centered rotation axes as well as the hollow site centered axes passing through the interstitial positions between the Ti and O atoms closest to the axes. The most stable [001]-oriented TiO2 NWs with rhombic cross sections are found to display the energetically preferable {110} facets only while the nanowires with quasi-square sections across the [110] axis are formed by the a…
Optical absorption of magnesia-supported gold clusters and nanoscale catalysts: Effects due to the support, clusters, and adsorbants
2005
Polarization-resolved optical spectra of magnesia-supported gold clusters ${\mathrm{Au}}_{N}∕\mathrm{Mg}\mathrm{O}$ $(N=1,2,4,8)$, bound at a surface color center ${F}_{s}$ of the MgO(100) face, are calculated from the time-dependent density functional theory. The optical lines for $N=1,2$ are dominated by transitions that involve strong hybridization between gold and ${F}_{s}$ states whereas for $N=4,8$ intracluster transitions dominate. The theoretical optical spectra are sensitive to cluster structure and adsorbants (here CO and ${\mathrm{O}}_{2}$ molecules on ${\mathrm{Au}}_{8}∕{F}_{s}@\mathrm{Mg}\mathrm{O}$) which suggests polarization-resolved optical spectroscopy as a powerful tool t…
A 'Butterfly'-shaped Water Tetramer in a Cu4 Complex Supported by a Hydrazone Ligand: Synthesis, Crystal Structure, Magnetic Properties, and Quantum …
2009
A potentially tetradentate NOOO donor hydrazone ligand, LH2 (condensation product of benzhydrazide with O-vanillin) generates a tetranuclear CuII complex [Cu4(L)4]·4H2O (1), whose void spaces are occupied by water tetramers presenting a ‘butterfly’ conformation with the highest dihedral angle reported to date, as revealed by its X-ray crystal structure. 1 has also been characterized using various spectroscopic techniques, including IR, UV-vis, and elemental analysis. Variable temperature magnetic susceptibility measurements reveal the presence of moderate antiferromagnetic intra-tetramer coupling between the four CuII centres connected through simple oxo groups of the hydrazone ligand with…
Evidence for an Intermediate in the Methylation of CB11H12−with Methyl Triflate: Comparison of Electrophilic Substitution in Cage Boranes and in Aren…
2013
The trideuteriomethylation of BH vertices in CB11H12− and its derivatives with CD3OTf (OTf=triflate, trifluoromethanesulfonate) yields a mixture of BCD3 and BCHD2 substitution products, thus demonstrating the intermediacy of a species with a long enough lifetime for hydrogen scrambling between the boron vertex and the methyl substituent. No such scrambling is observed if CD3OTf is used to methylate toluene. According to density functional theory calculations, the intermediate in BH vertex methylation is a three-center bonded σ adduct of a methyl cation to the BH bond and the proton scrambling occurs via a transition structure containing a distorted square-pyramidal methane attached axially …
Towards a lexicogrammatical pattern in Swedish crime novels
2013
The success of Swedish crime novels has been noted and discussed at length. Much of this commentary refers to a salient characteristic atmosphere which seems to be a common feature of most if not all Scandinavian crime novels. In this paper the potential of some recurring lexicogrammatical features to construct this characteristically gloomy and sombre atmosphere is presented and discussed. It will be shown that the vague feeling of unease which is perceived while reading these fictional texts is linguistically attestable. The analysis is conducted within the framework of M.A.K. Halliday’s systemic-functional grammar (SFG) which will be applied to three contemporary Swedish crime novels by …