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The interaction of ferrocene-1,1′-dithiol (FDT) with two parallel Ag(111) surfaces has been theoretically studied at density-functional level. The effect of surface defects on the energetic and electronic structure was investigated. The electronic transport properties are studied with the nonequilibrium Green’s function approach. The adsorption geometry has a strong effect on the electronic levels and conductivity. The presence of point defects strongly enhances the molecule-surface interaction but has a surprisingly small effect on the density of states near the Fermi energy. The FDT-surface bond is particularly strong near terraces or steps and leads to significant shifts of the molecular orbitals relative to the gas phase. For all considered defect types except the single adatom the electronic conductivity through the FDT molecule is decreased compared to adsorption on perfect surfaces. [ABSTRACT FROM AUTHOR]

Using density functional calculations, we show that the adsorption of ferrocene dithiol on the Ag(111) surface is remarkably flexible, i.e., a large number of different configurations have binding energies that differ by less than 0.1 eV per molecule. The thiolate bond is slightly favored over the thiol bond (by less than 0.1 eV) but may not be formed due to considerable activation barriers. Electronically, we found that the thiolate bound molecule is conducting, whereas thiol bonds turn it into semiconducting. [ABSTRACT FROM AUTHOR]

Yellow LaBa 2 Ta 5 O 13 N 2 was successfully synthesized as phase-pure material crystallizing isostructurally to previously reported Ba 3 Ta 5 O 14 N and mixed-valence Ba 3 Ta V 4 Ta IV O 15 . The electronic structure of LaBa 2 Ta 5 O 13 N 2 was studied theoretically with the range-separated hybrid method HSE06. The most stable structure was obtained when lanthanum was placed on 2 a and nitrogen on 4 h sites confirming Pauling's second rule. By incorporating nitrogen, the measured band gap decreases from ∼3.8 eV for the oxide via 2.74 eV for Ba 3 Ta 5 O 14 N to 2.63 eV for the new oxide nitride, giving rise to an absorption band well in the visible-light region. Calculated fundamental band gaps confirm the experimental trend. The atom-projected density of states has large contributions from N2p orbitals close to the valence band edge. These are responsible for the observed band gap reduction. Photocatalytic hydrogen formation was investigated and compared with that of Ba 3 Ta 5 O 14 N revealing significantly higher activity for LaBa 2 Ta 5 O 13 N 2 under UV-light. [ABSTRACT FROM AUTHOR]

Light yellow Ba 3 Ta V 5 O 14 N was successfully synthesized as phase-pure material crystallizing isostructurally to well-known mixed-valence Ba 3 Ta V 4 Ta IV O 15 . The electronic structure of Ba 3 Ta 5 O 14 N was studied theoretically with a hybrid Hartree–Fock-DFT method. The most stable structure was obtained when nitrogen atoms were placed at 4 h sites having fourfold coordination. By incorporating nitrogen, the band gap decreases from ∼3.8 eV commonly known for barium tantalum(V) oxides to 2.8 eV for the oxide nitride, giving rise to an absorption band well in the visible-light region. Ba 3 Ta 5 O 14 N was also tested for photocatalytic hydrogen formation. [ABSTRACT FROM AUTHOR]

The dissociation of water adsorbed on the surface of NiO was investigated by using the semi-empirical SCF MO method MSINDO. Simulations were based on embedded cluster models representing the (100) surface, with and without a monatomic step. The angle formed between the metal adsorption site and the O–H bond associated with water has been found to be critical to the energetics of the dissociation process. Based on this criterion, it was shown that water dissociation is favorable on the stepped surface, but highly unlikely on the planar surface. In addition, the activation energy required for water dissociation in a monatomic NiO step was considerably lower than for dissociation at the planar surface. The high activation energy associated with water dissociation on the planar surface is attributed to the rigidity of the NiO lattice. [ABSTRACT FROM AUTHOR]

The results of calculations of the phonon dispersion, the vibrational density of states and the heat capacity of lithium tetraborate and lithium triborate crystals are presented. They are obtained in the framework of a potential model that takes into account the non-equivalence of boron atoms in different structural positions (BO3 and BO4 units). A symmetry analysis of the phonon modes at G point was performed, and calculated frequencies are compared to experimental spectra. Analysis of Li contributions to the vibrational density of states reveals that the Li-O bonds in both crystals are relatively weak. This is in line with the experimentally observed high mobility of lithium ions at high temperatures. A good agreement between calculated and measured heat capacities from the literature was obtained. [ABSTRACT FROM AUTHOR]

Ab initio calculations allow to distinguish boron atoms in BO3 and BO4 complexes in lithium borates. On this basis an effective potential model for single crystals of Li2O-B2O3 is suggested. Empirical parameters of the interaction potentials are optimized in order to reproduce the experimental data of lithium tetraborate. The optimized parameters are applied to calculations of the structures of the anhydrous borate single crystals Li3BO3, LiBO2, Li2B4O7, Li3B7O12 and LiB3O5. The range of applicability of the potential model is increased by introducing a dependence of the effective oxygen charges on the Li content. In this way good agreement with experimental data is obtained for calculated structural and elastic properties. [ABSTRACT FROM AUTHOR]

Phase-pure Ba3TaV5O14N is prepared via a sol-gel based Pechini route by heating (200 °C) a 3:5 molar mixture of BaCl2 and TaCl5 in EtOH/citric acid/ethylene glycol prior to calcination at 400 °C. [ABSTRACT FROM AUTHOR]

Focuses on the July 2005 issue of the "Theoretical Chemistry Accounts" journal which is dedicated to chemist Karl Jug, who celebrated his 65th birthday in June 2005. Career background of Jug; Influence of Karl Jug in many fields of theoretical and computational chemistry which cover a large area of quantum chemistry.

Anion diffusion was simulated in the system (Y0.2Zr0.8)-(O1.72N0.15) with the molecular dynamics (MD) technique using the program DL_POLY, employing empirical potentials of the Buckingham type. To describe nitrogen migration, nitrogen potentials had to be developed, assuming the interaction of charged nitrogen shells with a mass of 0.15 amu with cores. Comparing experimental and simulated anion diffusivities, the diffusion coefficients were found to be of similar order. However, nitrogen diffuses five times slower than oxygen according to the computer simulation, while experimentally, the difference is reported to be smaller. Calculated activation enthalpies were 1.2 and 1.4 eV, respectively, for the two elements, with pre-exponential factors of 10-5 and 10-4 cm2/s, respectively. [ABSTRACT FROM AUTHOR]

The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information. [ABSTRACT FROM AUTHOR]

Abstract: Stability of B1 and B2 phases of Mg x Cd1−x O is studied by calculating the formation energy within the framework of density functional theory applying the crystalline-orbital program package. Structural and electronic properties of the two polymorphs are reported for x=0.25, 0.50 and 0.75. The equilibrium lattice constants and bulk moduli are computed. Enthalpy calculations show pressure induced B1→B2 phase transitions at 92GPa, 138GPa and 212GPa, respectively, for Mg0.25Cd0.75O, Mg0.50Cd0.50O and Mg0.75Cd0.25O compositions. Formation energy of ternary oxides in the B1 phase is negative with respect to mixing of B2-MgO with B1-CdO. Mixing B1-MgO with B2-CdO also leads to negative formation energy in Cd rich B1 phase ternary oxides (0≤x≤0.5). Band structure calculations predict direct band gaps in the B1 phase and indirect band gaps in the B2 phase ternary oxides. Mulliken population analysis is performed for the two polymorphs to study the charge transfer. [Copyright &y& Elsevier]

The normal incidence x-ray standing wave (NIXSW) technique is used to determine the adsorption geometry of submonolayer 3,4,9,1 0-perylene tetracarboxylic dianhydride (PTCDA) adsorbed on the Ag( 110) surface. An accurate analysis of both C1s and O1s photoemission (PE) spectra allows the respective adsorption heights of carbon and oxygen atoms in different chemical environments within PTCDA to be distinguished. Due to the intricacy of the PE fitting models, a systematic error analysis of NIXSW structural parameters was developed and employed. Based on the adsorption geometry of PTCDA on Ag( 110) a bonding mechanism is discussed. [ABSTRACT FROM AUTHOR]

A metastable bixbyite-type polymorph of vanadium sesquioxide, V2O3, has recently been synthesized, and it transforms to the corundum-type phase at temperatures around 550 °C. The possibility of a paramagnetic to canted antiferromagnetic or even spin-glass-like transition has been discussed. Quantum-chemical calculations on the density-functional theory level including explicit electronic correlation confirm the metastability as well as the semiconducting behavior of the material and predict that the bixbyite-type structure is about 0.1 eV less stable than the well-known corundum-type phase. Nonetheless, quasiharmonic phonon calculations manifest that bixbyite-type vanadium sesquioxide is a dynamically stable compound. Other possible V2O3 polymorphs are shown to be even less suitable candidates for the composition V2O3. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The reaction of either V2F6∙4H2O or a mixture of 60 wt % VF2∙4H2O and 40 wt % VF3∙3H2O with a water-saturated gaseous mixture of 15-20 vol % hydrogen in argon leads to the formation of a new polymorph of V3O5 crystallizing in the orthorhombic anosovite-type structure. Quantum-chemical calculations show that the anosovite-type structure is about 15 kJ/mol less stable than the corresponding monoclinic Magnéli phase. In addition, there are no imaginary modes in the phonon density of states, supporting the classification of the anosovite-type phase as a metastable V3O5 polymorph. Susceptibility measurements down to 3 K reveal no hint for magnetic ordering. [ABSTRACT FROM AUTHOR]

Abstract: The competitive interaction of chloride and SPS (bis-(sodium-sulfopropyl)-disulfide) at Cu(100)/electrolyte model interfaces was studied by means of cyclic voltammetry in combination with in situ STM and DFT. This specific anion/anion interaction is of paramount importance for the suppressor ensemble deactivation in the context of the industrial Cu Damascene process used for the state-of-the-art on-chip metallization. It is the interplay between chemisorbed chloride and SPS which regulates the dissociative SPS adsorption on copper as the key step in the course of the surface-confined MPS (mercaptopropane sulfonic acid) production. The latter species is considered as the actual anti-suppressor (depolarizer) in context of the Cu Damascene process. Under competitive conditions the chloride adsorbs and orders much faster on Cu(100) than the SPS. The resulting c(2×2)-Cl adlayer acts as an effective barrier for the dissociative SPS adsorption, at least under non-reactive conditions. Defect sites within the chloride matrix are identified as crucial pre-requisites for the dissociative SPS adsorption. Defects are generated under reactive conditions during copper dissolution or copper deposition due to rapid anion adsorption/desorption dynamics. As consequence of the SPS dissociation a mixed, defect-rich c(2×2)-Cl–MPS co-adsorption phase forms on Cu(100) where every second chloride species of the pristine c(2×2)-Cl adlayer is displaced by MPS units. This co-adsorption phase reveals an apparent p(2×2) symmetry in the STM experiment since only the sulfonic head groups of the MPS units are imaged while the S and the Cl species chemisorbed on the copper surface remain invisible at the “buried” interface. The relevance of this surface reaction for the Cu Damascene process is discussed in detail. [Copyright &y& Elsevier]

A metastable polymorph of vanadium sesquioxide was prepared by the reaction of vanadium trifluoride with a water-saturated gaseous mixture of 10 vol % hydrogen in argon. The new polymorph crystallizes in the bixbyite-type structure. At temperatures around 823 K a transformation to the well-known corundum-type phase is observed. Quantum-chemical calculations show that the bixbyite-type structure is about 9 kJ/mol less stable than the known corundum-based one. This result, in combination with the absence of imaginary modes in the phonon density of states, supports the classification of the bixbyite-type phase as a metastable V2O3 polymorph. At ~ 50 K a paramagnetic to canted antiferromagnetic transition is detected. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of electronic structure of the organic semiconductor iron-phthalocyanine with potassium doping has been studied by means of photoemission spectroscopy, near-edge X-ray absorption fine structure and density functional theory (DFT) calculations. The DFT study and detailed analysis of the core-level spectra permit us to suggest possible lattice sites for the potassium ions. The data disclosed filling of the lowest unoccupied molecular orbital upon doping and associated changes of the core level absorption spectra. None of the films prepared in our studies showed a finite electronic density of states at the Fermi level. [Copyright &y& Elsevier]

The electronic structure and morphology of organic semiconducting cobalt-phtalocyanine (CoPc) films in situ prepared on the Au(001)-5×20 superstructure have been studied by a combination of experimental and theoretical work. The CoPc molecular film was characterized by photoemission spectroscopy (PES, valence band and core-level). The experimental results were simulated and have been explained in the framework of density functional theory (DFT) calculations. The C 1 s and N 1 s core level spectra were analyzed by taking into account the fact that both types of atoms have different nonequivalent positions in the molecule. And finally, the experimentally obtained electronic valence band structure of CoPc is in very good agreement with ab initio density of state results, allowing a detailed site-specific insight into the system. [ABSTRACT FROM AUTHOR]

Abstract: The filled and unoccupied electronic states of the organic semiconductor copper-phthalocyanine (CuPc) have been determined by a combination of direct and resonant photoemission, near-edge X-ray absorption and first principles calculations. The experimentally obtained electronic states of CuPc are in very good agreement with results of ab initio density of states, allowing to derive detailed site specific information. [Copyright &y& Elsevier]

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO1 – x S x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium doped tantalum oxynitrides were prepared by ammonolysis of amorphous mixed oxides. An orange colored anatase-type phase with the composition Mg0.05Ta0.95O1.15N0.85 was found. It is metastable and undergoes a phase transformation to a baddeleyite-type phase between 900 and 1000°C. X-ray diffraction measurements indicate spacegroup I41/amd with lattice parameters and . A possible anion ordering was examined by theoretical methods and neutron diffraction experiments. In addition, anosovite-type (Ti3O5) phases Mg x Ta3− x O3 x N5−3 x ; 0⩽x⩽0.3 were obtained. The electronic spectra of all phases were investigated by UV/vis spectroscopy. [Copyright &y& Elsevier]

Abstract: Adsorption of simple organic molecules on wide band gap insulators is a versatile tool to introduce unoccupied electronic states in the band gap at the surface. Relative energetic positions, varied also by intra-molecular interactions of functional side groups, determine the effective band gap. Specific examples used here are adsorbed molecules of benzoic acid and of its OH-substituted derivates (salicylic acid, etc.) on NaCl, KCl and on MgSO4 ·H2O. These acids are mainly physisorbed on NaCl and KCl, whereas on MgSO4 ·H2O chemical bond formation is found. Ab initio and semi-empirical calculations are used in order to identify mechanisms of surface-molecule as well as intra-molecular interactions. [Copyright &y& Elsevier]

The new anosovite-type polymorph of the title compound is synthesized by reaction of either V2F6·4H2O or a mixture of 60 wt.% VF2·4H2O and 40 wt.% VF3·3H2O with a flowing water-saturated gaseous mixture of 15-20 vol% H2 in argon (588 K, 14-18 h). [ABSTRACT FROM AUTHOR]