Li Diffusion in Various Polymorphs of LiTiS2: Insights from Theory

In the present contribution, the stoichiometric and defect properties in 1T, c and 3R polymorphs of lithium titanium disulphide (LixTiS2) are investigated theoretically with periodic quantum chemical methods

Kreditverkäufe in der Praxis : Missbrauchsfälle und aktuelle Reformansätze

Der Verkauf von Immobiliendarlehen sorgt nach wie vor für Aufregung. Die Kreditwirtschaft sieht sich mit vehementen öffentlichen Vorwürfen konfrontiert, die den Kredithandel beeinträchtigen. Die Kreditinstitute werden indes nicht müde in ihren Beteuerungen, ordnungsgemäß bediente Kredite nicht an Finanzinvestoren zu veräußern und dabei hinzunehmen, dass ihre Kreditnehmer ihrer Wohnimmobilie verlustig gehen. Die praktische Bedeutung des Kredithandels ist gerade in Deutschland immens. Exemplarisch genannt sei als eine der größten bisherigen Transaktionen der Ende 2007 erfolgte Erwerb eines 53.000 Immobiliarkredite umfassenden Portfolios im Volumen von ca. 4,3 Mrd. Euro durch die ING Diba von der Hypo Real Estate. Unter der Überschrift "Verbesserte Transparenz bei Verkäufen von Kreditforderungen" hat die Bundesregierung um die letzte Jahreswende ein Maßnahmenpaket vorgelegt, mit dem auf Missbrauchsfälle beim Verkauf von Krediten reagiert werden soll. Inzwischen ist die Diskussion fortgeschritten, weitere Reformvorschläge sind in der Welt. Dabei sind die rechtlichen Rahmenbedingungen von Kreditverkäufen de lege lata auch nach einer einschlägigen BGH-Entscheidung vom 27. Februar 2007 noch immer nicht abschließend geklärt. Bevor in nachfolgendem Beitrag die aktuellen Reformansätze vorgestellt und einer kurzen Bewertung unterzogen werden, seien daher die derzeitige Praxis und Rechtslage untersucht

Enhanced conductivity at the interface of Li2O:B2O3 nanocomposites: Atomistic models

A theoretical investigation at density-functional level of Li ion conduction at the interfaces in Li2O:B2O3 nanocomposites is presented. The structural disorder at the Li2O(111):B2O3(001) interface leads to reduced defect formation energies for Li vacancies and Frenkel defects compared to Li2O surfaces. The average activation energy for Li+ diffusion in the interface region is in the range of the values for Li2O. It is therefore concluded that the enhanced Li conductivity of Li2O:B2O3 nanocomposites is mainly due to the increased defect concentration. © 2007 The American Physical Society

The Effects of Oxidation States, Spin States and Solvents on Molecular Structure, Stability and Spectroscopic Properties of Fe-Catechol Complexes: A Theoretical Study

In this study, in order to explain the solvent and spin state effects on the molecular structure of catechol-Fe complex [Fe(cat)3]n﹣ where n = 2 and 3, Hartree Fock (HF)-Density Functional Theory (DFT) hybrid calculations are performed at the B3LYP/6-311g(d,p) level of theory. The binding energies of Fe2+ and Fe3+ in high-spin state are higher than intermediate and low-spin states which show that the complex formation in a high spin state is more favorable. The calculated binding energies at different solvents indicate that the binding energies in polar solvents are lower than non-polar solvents. Furthermore, spectroscopic studies including FTIR and Raman spectrum in various solvents reveal that the formation of intermolecular bonds between the oxygen atom of carbonyl group and the hydrogen atom of solvent causes a spectral red shift. The calculated FTIR and geometry parameters are in good agreement with previous experimental data. Donor-acceptor interaction energies are evaluated due to the importance of the charge transfer in the complex formation. It is observed that the free electrons of oxygen atom interact with the antibonding orbitals of the iron. Finally, some correlations between the quantum chemical reactivity indices of the complexes and solvent polarity are considered. The study indicates a linear correlation between chemical hardness and binding energies of [Fe(cat)3]3﹣ complex.Regional Scientific Computing Center for Lower Saxony (RRZN

Structural, vibrational and electronic properties of SnMBO4 (M = Al, Ga): A predictive hybrid DFT study

We propose two new members of the mullite-type family, SnAlBO4 and SnGaBO4, and carry out an in-depth study of their crystal properties using the hybrid method PW1PW. Both are isostructural to PbMBO4 (M = Fe, Mn, Al, Ga), which show axial negative linear compressibility (ANLC), among other interesting features. We find that, although Sn2+ is susceptible of being oxidized by oxygen, a suitable range of experimental parameters exists in which the compounds could be synthesized. We observe absence of ANLC below 20 GPa and explain it by the small space occupied by the lone electron pairs, as indicated by the small length of the corresponding Liebau Density Vectors. In agreement with this fact, the structures present a low number of negative mode-Grüneisen parameters, which may also suggest lack of negative thermal expansion. The electronic properties show a remarkable anisotropic behaviour, with a strong dependence of the absorption spectra on light polarization direction

Density Functional Theory Evaluated for Structural and Electronic Properties of 1T-LixTiS2 and Lithium Ion Migration in 1T-Li0.94TiS2

In many applications it has been found that the standard generalized gradient approximation (GGA) does not accurately describe weak chemical bond and electronic properties of solids containing transition metals. In this work, we have considered the intercalation material 1T-LixTiS2 (0≤x≤1) as a model system for the evaluation of the accuracy of GGA and corrected GGA with reference to the availabile experimental data. The influence of two different dispersion corrections (D3 and D-TS) and an on-site Coulomb repulsion term (GGA+U) on the calculated structural and electronic properties is tested. All calculations are based on the Perdew-Burke-Ernzerhof (PBE) functional. An effective U value of 3.5 eV is used for titanium. The deviation of the calculated lattice parameter c for TiS2 from experiment is reduced from 14 % with standard PBE to −2 % with PBE+U and Grimme’s D3 dispersion correction. 1T-TiS2 has a metallic ground state at PBE level whereas PBE+U predicts an indirect gap of 0.19 eV in agreement with experiment. The 7Li chemical shift and quadrupole coupling constants are in reasonable agreement with the experimental data only for PBE+U-D3. An activation energy of 0.4 eV is calculated with PBE+U-D3 for lithium migration via a tetrahedral interstitial site. This result is closer to experimental values than the migration barriers previously obtained at LDA level. The proposed method PBE+U-D3 gives a reasonable description of structural and electronic properties of 1T-LixTiS2 in the whole range 0≤x≤1. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017

Lithium diffusion pathways in 3R-LixTiS2: a combined neutron diffraction and computational study

Layered lithium transition-metal sulfides have long been discussed as early electrode materials for lithium-ion batteries. However, fundamental knowledge of lithium-ion migration in these solids is still lacking. In this study, we report on the diffusion dynamics in lithium-deficient high-temperature polymorphs of lithium titanium sulfides (3R-LixTiS2; x = 0.7, 0.9) as analyzed using powder neutron diffractometry and density functional theory (DFT) climbing-image nudged-elastic-band (cNEB) calculations. Two classes of probable migration pathways have been identified from the scattering-length density distributions (filtered using the maximum-entropy method [MEM]) and the probability density functions (PDFs, modeled from anharmonic Debye-Waller factors): direct diffusion in the (001) plane as the major mechanism and indirect diffusion through adjacent tetrahedral voids as a minor mechanism. Calculated activation barriers agree well with one-particle potentials (OPPs) derived from measurements for Li0.7TiS2 (0.484[14] and 0.88[4] eV) but deviate for Li0.9TiS2. The discrepancy at low defect concentration is attributed to the failure of the OPP derivation and the different nature of the methods (space-time averaged vs individual-ion perspective). This work elucidates the pathways of lithium-ion diffusion in 3R-LixTiS2 and points out pitfalls in established experimental/computational methods.DFG, FOR 1277, Mobilität von Lithiumionen in Festkörpern (molife

Effect of Partial Replacement of Pt-Based Catalysts with Fe- and Co-for Oxygen Evolution Reaction in Pem Water Electrolysis: A Combined Theoretical and Experimental Study

The adsorption of Ptn (n = 1−4) clusters and co-adsorption of Ptn-Co and Ptn-Fe on the defect-free anatase TiO2(101) surface have been studied theoretically at density functional theory (DFT) level. The most stable configurations are observed due to Pt2 and Pt3-clusters adsorbed on the titania surface. The electronic structure analyses show that the Fermi level is pinned by Pt, which reduces the band gap from ~3 eV of the clean surface to significantly less than 1 eV for Pt3. For the co-adsorption of Fe-Pt and Co-Pt, there is a strong bond formation of Fe and Co with the surface O and Ti atoms. In both cases, Fe and Co stay far away from the Pt atom. Due to strong interaction of adsorbed elements with Ti, the co-adsorption energy is larger than the corresponding Pt3 adsorption energy. The higher stability of the co-adsorption of Fe-Ptn compared to the Co-Ptn is in agreement with the electrochemical experimental results which confirm that Fe-containing catalysts deposited on titanium dioxide support (Ebonex) will be higher efficient than Co-containing ones toward oxygen evolution in proton-exchange membrane water electrolysis. The observed effect can be explained with formation of solid solution between the metallic components and a realization of synergetic effect