Search results for "DF"
showing 10 items of 1699 documents
Pressure stability field of Mg-perovskite under deep mantle conditions: A topological approach based on Bader's analysis coupled with catastrophe the…
2019
Abstract The pressure stability field of the Mg-perovskite phase was investigated by characterizing the evolution of the electron arrangement in the crystal. Ab initio calculations of the perovskite structures in the range 0–185 GPa were performed at the HF/DFT (Hartree-Fock/Density Functional Theory) exchange–correlation terms level. The electron densities, calculated throughout the ab-initio wave functions, were analysed by means of the Bader's theory, coupled with Thom's catastrophe theory. To the best of our knowledge the approach is used for the first time. The topological results show the occurrence of two topological anomalies at P~20 GPa and P~110 GPa which delineate the pressure ra…
Co-doping with boron and nitrogen impurities in T-carbon
2020
Previously, Ren et al. [Chem. Phys. 518, 69–73, 2019] reported the failure of Boron-Nitrogen (B-N) co-doping as inter B-N bond in T-carbon. In present work, a B-N atom pair is introduced in T-carbon as p-n co-dopant to substitute two carbon atoms in the same carbon tetrahedron and form an intra B-N bond. The stability of this doping system is verified from energy, lattice dynamic, and thermodynamic aspects. According to our B3PW calculations, B-N impurities in this situation can reduce the band gap of T-carbon from 2.95 eV to 2.55 eV, making this material to be a promising photocatalyst. Through the study of its transport properties, we can also conclude that B-N co-doping cannot improve th…
Proton sponge lead halides containing 1D polyoctahedral chains
2021
Hybrid one-dimensional lead halides, containing the protonated 1,8-bis(dimethylamino)naphthalene moiety (C14H19N2, monoprotonated "proton sponge"), were prepared by simple one-pot methods and investigated in terms of crystal structure, morphology, thermal stability and electronic properties. The as-precipitated (C14H19N2)PbBr3 and (C14H19N2)PbI3 species are isostructural and crystallize in the orthorhombic Pbca space group, resulting in 1D crystal phases with ([PbX3](-))(infinity) chains (built by face-sharing [PbX6] octahedra; X = Br, I), among which the (C14H19N2)(+) cations are inserted. The two compounds display complete miscibility in the solid state: both (C14H19N2)PbI2Br and (C14H19N…
Out-of-plane transport of 1T-TaS2/graphene-based van der Waals heterostructures
2021
Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the in-plane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations. It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. In this system, the interlayer stacking of the CDW is crucial for the interpretation of the underlying electronic and magnetic phase diagram. Here, thin-layers of 1T-TaS2 are …
Friction Factor for Gravel-Bed Channel with High Boulder Concentration
2000
This paper reports the results of an experimental investigation on flow resistance law for a gravel-bed channel having bed arrangements characterized by different values of the number of boulders. The dependence is studied of a parameter, proposed for describing the gravel-bed surfaces, on the boulder concentration and on the ratio between the median diameter of the coarser particles and the median diameter of the bed layer. Flume measurements carried out for the hydraulic condition of \Itransition\N and \Ilarge-scale\N roughness (1.5 ≤ \ih/\id\d5\d0 ≤ 6.9) show that the intercept of the semilogarithmic flow resistance law depends on the ratio and on boulder concentration. For concentration…
Structural and Mössbauer study of (Sb0.70Te0.30)100-x Snx alloys with x = 0, 2.5, 5.0 and 7.5
2019
(Sb 0.70 Te 0.30 ) 100-x Sn x alloys (with x = 0, 2.5, 5.0 and 7.5 at. %)have been synthesized and characterized in order to determine the crystalline structure and properties of materials obtained upon solidification and to extract information about the location of the Sn atom in the Sb-Te matrix. Powder X-ray diffraction (XRD)has been used to determine the crystalline structure, whereas Mössbauer spectroscopy has been utilized to determine the localization and the local structure of the Sn atom in the Sb-Te matrix through the hyperfine interactions of the 119 Sn probe with its environment. We found that Sb 70 Te 30 crystallizes in a trigonal structure belonging to P-3m1 space group, while…
Nitrogen Hydrate Cage Occupancy and Bulk Modulus Inferred from Density Functional Theory-Derived Cell Parameters
2021
International audience; Gas clathrate hydrate solid materials, ubiquitous in nature as found either on the ocean floor, permafrost on the Earth, or in extraterrestrial planets and comets, are also technologically relevant, for example, in energy storage or carbon dioxide sequestration. Nitrogen hydrate, in particular, is of great interest as a promoter of the kinetics of the methane replacement reaction by carbon dioxide in natural gas hydrates. This hydrate may also appear in the chemistry of planets wherever nitrogen constitutes the majority of the atmosphere. A fine understanding of the stability of this hydrate under various thermodynamic conditions is thus of utmost importance to asses…
DFT calculations on subnanometric metal catalysts: a short review on new supported materials
2018
Metal clusters have been used in catalysis for a long time, even in industrial production protocols, and a large number of theoretical and experimental studies aimed at characterizing their structure and reactivity, either when supported or not, are already present in the literature. Nevertheless, in the last years the advances made in the control of the synthesis and stabilization of subnanometric clusters promoted a renewed interest in the field. The shape and size of sub-nanometer clusters are crucial in determining their catalytic activity and selectivity. Moreover, if supported, subnanometric clusters could be highly influenced by the interactions with the support that could affect geo…
Strong chiral dichroism and enantiopurification in above-threshold ionization with locally chiral light
2021
We derive here a highly selective photoelectron-based chirality-sensing technique that utilizes “locally chiral” laser pulses. We show that this approach results in strong chiral discrimination, where the standard forwards/backwards asymmetry of photoelectron circular dichroism (PECD) is lifted. The resulting dichroism is larger and more robust than conventional PECD (especially in the high-energy part of the spectrum), is found in all hemispheres, and is not symmetric or antisymmetric with respect to any symmetry operator. Remarkably, chiral dichroism of up to 10% survives in the angularly integrated above-threshold ionization (ATI) spectra, and chiral dichroism of up to 5% survives in the…
Production of hydrogen negative ions in an ECR volume source: balance between vibrational excitation and ionization
2018
International audience; The operation of an ECR-driven (2.45 GHz) hydrogen negative ion source is studied. Electron densities and temperatures are investigated with electrostatic probes and negative ion densities are measured with laser photodetachment. Vacuum ultraviolet irradiance measurements are focused on molecular transitions to the ground state while high-resolution visible emission spectroscopy is used to study the transitions between excited states for both molecules and atoms. The standalone operation of the source is found to be more efficient in higher pressures (12 mTorr) where negative ion densities are as high as 4×109 cm−3. Further investigation on the operation of the sou…