2012年6月-Materials Studio文献参考

时间:2014-01-07

DMol3 + Discovery Studio

Molecular Dynamics Simulation Study and Hybrid Pharmacophore Model Development in Human LTA4H Inhibitor Design

Human leukotriene A4 hydrolase (hLTA4H) is a bi-functional enzyme catalyzes the hydrolase and aminopeptidase functions upon the fatty acid and peptide substrates, respectively, utilizing the same but overlapping binding site. Particularly the hydrolase function of this enzyme catalyzes the rate-limiting step of the leukotriene (LT) cascade that converts the LTA4 to LTB4. This product is a potent pro-inflammatory activator of inflammatory responses and thus blocking this conversion provides a valuable means to design anti-inflammatory agents. Four structurally very similar chemical compounds with highly different inhibitory profile towards the hydrolase function of hLTA4H were selected from the literature. Molecular dynamics (MD) simulations of the complexes of hLTA4H with these inhibitors were performed and the results have provided valuable information explaining the reasons for the differences in their biological activities. Binding mode analysis revealed that the additional thiophene moiety of most active inhibitor helps the pyrrolidine moiety to interact the most important R563 and K565 residues. The hLTA4H complexes with the most active compound and substrate were utilized in the development of hybrid pharmacophore models. These developed pharmacophore models were used in screening chemical databases in order to identify lead candidates to design potent hLTA4H inhibitors. Final evaluation based on molecular docking and electronic parameters has identified three compounds of diverse chemical scaffolds as potential leads to be used in novel and potent hLTA4H inhibitor design.

http://dx.doi.org/10.1371/journal.pone.0034593

CASTEP

Hydrogen stabilization of metallic vanadium dioxide in single-crystal nanobeams

Vanadium dioxide is a strongly correlated material1234 that undergoes a metal–insulator transition5 from a high-temperature, rutile metal to a monoclinic insulating state at 67 °C. In recent years, experiments on single-crystal vanadium-dioxide nanowires grown by physical vapour deposition6 have shed light on the crucial role of strain in the structural and electronic phase diagram of this material78910, including evidence for a new M2 phase1112, but the detailed physics of this material is still not fully understood. The transition temperature can be reduced by doping with tungsten813, but this process is not reversible. Here, we show that the metal–insulator transition in nanoscale beams of vanadium dioxide can be strongly modified by doping with atomic hydrogen14 using the catalytic spillover method15. We also show that this process is completely reversible, and that the metal–insulator transition eventually vanishes when the doping exceeds a threshold value. Raman and conventional optical microscopy, electron diffraction and transmission electron microscopy provide evidence that the structure of the metallic post-hydrogenation state is similar to that of the rutile state. First-principles electronic structure calculations confirm that a distorted rutile structure is energetically favoured following hydrogenation, and also that such doping favours metallicity from both the Mott and Peierls perspectives. We anticipate that hydrogen doping will be a powerful tool for examining the metal–insulator transition and for engineering the properties of vanadium dioxide.

http://dx.doi.org/10.1038/NNANO.2012.70

 

Structural and Electronic Properties of T Graphene: A Two-Dimensional Carbon Allotrope with Tetrarings

T graphene, a two-dimensional carbon allotrope with tetrarings, is investigated by first-principles calculations. We demonstrate that buckled T graphene has Dirac-like fermions and a high Fermi velocity similar to graphene even though it has nonequivalent bonds and possesses no hexagonal honeycomb structure. New features of the linear dispersions that are different from graphene are revealed. πand π* bands and the two comprising sublattices are the key factors for the emergence of Dirac-like fermions. T graphene and its two types of nanoribbon are expected to possess additional properties over graphene due to its different band structure.

http://dx.doi.org/10.1103/PhysRevLett.108.225505

Experimental and theoretical study of Ti-6Al-4V to 220 GPa

We report results from an experimental and theoretical study of the ternary alloy Ti-6Al-4V to 221 GPa. We observe a phase transition to the hexagonal ω phase at approximately 30 GPa, and then a further transition to the cubic β phase starting at 94–99 GPa. We do not observe the orthorhombic γ and δ phases reported previously in pure Ti. Computational studies show that this sequence is possible only if there is significant local atomic ordering during the compression process, yet insufficient atomic diffusion to reach the phase-separated thermodynamic equilibrium state.

http://dx.doi.org/10.1103/PhysRevB.85.224202

Relative strength of phase stabilizers in titanium alloys

Titanium alloys exhibit three distinct crystal structures: αβ, and ω. For various applications alloying elements can be used to stabilize the desired phase. Extensive data exist to determine the thermodynamic equilibrium phase, typically phase coexistence. However, the normal state of commercial alloys is a quenched solid solution. While alloy designers have well-established rules of thumb, rigorous theory for nonequilibrium single-phase crystal stability is less well established. We develop a theory to predict which phase a particular alloy will adopt, as a function of minor element concentration. We use two different methods based on density functional theory with pseudopotentials and plane waves, with either explicit atoms or the virtual crystal approximation (VCA). The former is highly reliable, while the latter makes a number of drastic assumptions that typically lead to poor results. Surprisingly, the agreement between the methods is good, showing that the approximations in the VCA are not important in determining the phase stability and elastic properties. This allows us to generalize, showing that the single-phase stability can be related linearly to the number of d electrons, independent of the actual alloying elements or details of their atomistic-level arrangement. This leads to a quantitative measure of β stabilization for each alloying transition metal.

http://dx.doi.org/10.1103/PhysRevB.85.214106

 

Structure, elasticity, thermodynamics and high pressure behavior of ZnB4O7and CdB4O7

An accurate single crystal determination of the structure of α-ZnB4O7 is reported, and an improved description of the polyhedral network is presented. The experimental data are used to evaluate density functional theory calculations. Structural models based on the PBESOL exchange-correlation functional were in slightly better agreement with experimental data than those employing the PBE exchange-correlation functional. However, in both cases the agreement between the results of the experiments and the calculations was very satisfactory. The models were therefore used to predict the compression behavior (Bα-4ZnBO7=59.9(7) GPa), the elasticity tensor, bond populations, and a transition pressure of 3.7 GPa for the transition into the high pressure β-phase. The predicted bulk modulus of the high pressure polymorph is Bβ-4ZnBO7=210.4(4) GPa. The heat capacity of the α-phase has been determined with quasi-adiabatic microcalorimetric measurements and at low temperatures a Debye temperature of Θ = 787 K has been obtained. The results obtained for α- and β-ZnB4O7 are compared to those of the isostructural CdB4O7 compounds. The transition from the α- to a high pressureβ-phase of CdB4O7 is predicted to occur at ≈1.9 GPa, but within the uncertainty of the model, the high pressure phase may also be isostructural to β-CaB4O7.

http://dx.doi.org/10.1016/j.solidstatesciences.2012.05.008

First-principles study of the effect of heavy Ni doping on the electronic structure and absorption spectrum of wurtzite ZnO

The band structures, densities of states and absorption spectra of pure ZnO and two heavily Ni doped supercells of Zn0.9722Ni0.0278O and Zn0.9583Ni0.0417O have been investigated using the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory. The calculated results showed that the band gap is narrowed by Ni doping in ZnO; this, is because the conduction band undergoes a greater shift toward the low-energy region than the valence band and because heavier doping concentrations lead to, narrower band gaps. Moreover, the optical absorption edge exhibits a redshift due to the narrowing of the band gap. Heavier doping concentrations leads to more significant redshifts, which is in agreement with the experimental results.

http://dx.doi.org/10.1016/j.physb.2012.02.030

 

Mechanical properties and electronic structure of TiC, Ti0.75W0.25C, Ti0.75W0.25C0.75N0.25, TiC0.75N0.25 and TiN

The first-principles calculations are performed to investigate the mechanical properties and electronic structure of TiC, Ti0.75W0.25C, Ti0.75W0.25C0.75N0.25, TiC0.75N0.25 and TiN. Density functional theory and ultrasoft pseudopotentials are used in this study. From the formation energy, it is found that nitrogen can increase the stability of TiC. The calculated elastic constants and elastic moduli of TiC compare favorably with other theoretical and experimental values. Tungsten and nitrogen are observed to significantly increase the bulk, shear and Young's modulus of TiC. Through the analysis of B/G and Cauchy pressure, tungsten can significantly improve the ductility of TiC. The electronic structure of TiC, TiN, Ti0.75W0.25C, Ti0.75W0.25C0.75N0.25, and TiC0.75N0.25 are used to describe nonmetal–metal and metal–metal bonds. Based on the Mulliken overlap population analysis, the hardness values of TiC, Ti0.75W0.25C, Ti0.75W0.25C0.75N0.25, TiC0.75N0.25 and TiN are estimated.

http://dx.doi.org/10.1016/j.physb.2012.03.064

First-principles study on the elastic property of hexagonal alunite

In this paper, we have predicted the structural and elastic characteristics of KAl3(SO4)2(OH)6 compounds through the method of density functional theory within the generalized gradient approximation (GGA) and Local Density Approximation (LDA) using the CASTEP package. The calculated equilibrium lattice parameters, the elastic property, anisotropy factor, Poison's ratio, Young's modulus, sound velocities and Debye temperature for KAl3(SO4)2(OH)6 have been calculated and compared with the available experimental data. From these results, this compound behaves as a brittle material and has a good thermal conductivity.

http://dx.doi.org/10.1016/j.physb.2012.04.004

 

Effects of surface structure and Ag–Sb nanodots on electronic properties of PbTe (1 0 0) facets from first-principles calculations

Based on the DFT theory and first-principles calculations, we found that both the oscillatory relaxed surface geometry and Ag–Sb doping configuration exert prominent effects on the electronic properties and doping stability of an Ag–Sb co-doped PbTe (1 0 0) surface. Ag and Sb atoms tend to form Ag–Sb nanodots in the subsurface layers and the thermoelectric performance of PbTe may be improved through Ag–Sb doping into PbTe thin film due to the enhancement and distortion of the density of states near the Fermi level.

http://dx.doi.org/10.1016/j.scriptamat.2012.03.010

Crystal Structure of High-Pressure Phases V and VI of Potassium Dihydrogen Phosphate

Potassium dihydrogen phosphate KH2PO4 is the most typical hydrogen-bonded ferroelectric. The PT phase diagram and the existence of high-pressure phases V and VI have already been reported. However, their crystal structures remain unknown. We performed a powder x-ray diffraction experiment under high pressure using synchrotron radiation and analyzed the structures from the obtained data. The structures of phases V and VI were determined to be orthorhombic C2221 and triclinic P\bar1. Their hydrogen positions were predicted by a density functional theory calculation.

http://dx.doi.org/10.1143/JPSJ.81.064706

Electronic and optical properties of distorted rare-earth manganite under hydrostatic pressure

The effect of hydrostatic pressure on the crystal structure, electronic and optical properties of distorted rare-earth manganite TbMnO3 has been studied on the basis of first-principle calculations. The results reveal that the band gaps reduce quadratically with increasing pressure. The optical properties of TbMnO3 predict that the peaks in the dielectric function shift to higher photon energy due to the transformation of inner electronic states with increasing pressure. Otherwise, the peaks in the reflectivity spectra and loss function were also found to move to higher photon energy with pressure increasing and the relationships between the positions of these peaks and pressure can be fitted by third order polynomial expressions.

http://dx.doi.org/10.1016/j.ssc.2012.03.024

 

First-principles calculations of Cd-doped ZnO thin films deposited by pulse laser deposition

Zn1−xCdxO thin films are deposited on quartz substrate by pulse laser deposition. Their band structure and optical properties are experimentally and theoretically investigated. By varying Cd concentration, the band gap of Zn1−xCdxO films can be adjusted in a wide range from 3.219 eV for ZnO to 2.197 eV for Zn0.5Cd0.5O, which produces different emissions from ultraviolet to Kelly light in their photoluminescence spectra. Simultaneity, the electronic structure and band gap of Zn1−xCdxO are investigated by the density functional theory (DFT) with a combined generalized gradient approximation (GGA) plus Hubbard U approach, which precisely predicts the band-gaps of ZnO and Zn1−xCdxO alloys. Both the experimental results and theoretical simulation reveal that with increasing Cd concentration in Zn1−xCdxO alloys, their absorption coefficients in visible light range are evidently enhanced. The adjustable photoluminescence emission and enhanced visible light absorption endow Zn1−xCdxO alloys potential applications in optoelectronic and photocatalytic fields.

http://dx.doi.org/10.1016/j.solidstatesciences.2012.03.018

Structure, Elastic Stiffness, and Hardness of Os1–xRuxB2 Solid Solution Transition-Metal Diborides

On the basis of recent experiments, the solid solution transition-metal diborides were proposed to be new ultra-incompressible hard materials. We investigate using density functional theory based methods the structural and mechanical properties, electronic structure, and hardness of Os1–xRuxB2 solid solutions. A difference in chemical bonding occurs between OsB2 and RuB2 diborides, leading to significantly different elastic properties: a large bulk, shear moduli, and hardness for Os-rich diborides and relatively small bulk, shear moduli, and hardness for Ru-rich diborides. The electronic structure and bonding characterization are also analyzed as a function of Ru–dopant concentration in the OsB2 lattice.

http://dx.doi.org/10.1021/jp3015657

First-principles LDA + U calculations investigating the lattice contraction of face-centered cubic Pu hydrides

Plutonium metal can be loaded with hydrogen, which forms complicated solid solutions and compounds, and leads to significant changes in electronic structure. A first-principles pseudopotential plane wave method with added Hubbard parameterU was employed to investigate the electronic and structural properties of face-centered cubic Pu hydrides (PuHxx = 2, 2.25, and 3). The decrease in calculated lattice parameters with increasing x is in reasonable agreement with experimental findings. Comparative analysis of the electronic-structure results for a series of PuHx compositions reveals that lattice contraction occurs due to enhanced chemical bonding and the size effects involving interstitial atoms. We find that the size effects are the driving force for the abnormal lattice contraction.

http://dx.doi.org/10.1016/j.jnucmat.2012.03.001

 

CASTEP NMR

 

Effects of Aromatic Substitution on the Photodimerization Kinetics of β-trans Cinnamic Acid Derivatives Studied with 13C Solid-State NMR

In our efforts to study photodimerizations in the solid state, we present data on the influence of the position of aromatic substitution by bromine on the photodimerization rate in cinnamic acid derivatives. Results were obtained by 13C CPMAS NMR spectroscopy together with chemical shift tensor analysis, DFT calculations using the NMR-CASTEP program, and crystal structure data. Reaction rates are highest for para bromo substitution, whose parent crystal structure was solved in this work. To explain the differences in photoreaction rate, several factors such as distance between double bonds, best π-orbital overlap of the reacting C═C double bonds, and CSA tensor analysis (using 2D PASS) were taken into account. Calculations of 13C chemical shifts and chemical shift anisotropy tensor parameters show very good agreement with experimental data, including the carboxylic carbon that is hydrogen bonded to the neighboring cinnamic acid molecule. For the cinnamic acid photodimerization, the best angle between reacting double bonds and the smallest degree of molecular reorientation favor faster photoreaction.

http://dx.doi.org/10.1021/jp301703d

Structural Investigation of α- and β-Sodium Hexafluoroarsenate, NaAsF6, by Variable Temperature X-ray Powder Diffraction and Multinuclear Solid-State NMR, and DFT Calculations

We report the phase transition between the α- and β-phases of NaAsF6 monitored by DTA, variable temperature 19F solid-state NMR and temperature controlled X-ray powder diffraction (XRPD) as well as their crystalline structures determined from XRPD data. The structural type of β-NaAsF6 has been determined thanks to 19F and75As solid-state NMR experiments. 19F, 23Na, and 75As NMR parameters, including19F–75As 1J coupling, have been measured for both phases. The 19F, 23Na, and75As solid-state NMR investigations are in full agreement with both crystalline structures from a qualitative point of view. Chemical shielding tensors have been calculated from the gauge including projector augmented wave approach. The electric field gradient tensors of 23Na and 75As have been calculated in α-NaAsF6from the all-electrons method and the projector augmented-wave approach. Two difficulties were encountered: the libration of the rigid and regular AsF6 anions in the β-phase, highlighted by the atomic anisotropic displacement parameters for F, which leads to erroneous shortened As–F bond length, and the overestimation of the As–F bond length with the PBE functional used in the density functional theory calculations. We show that both difficulties can be overcome by full optimization and rescaling of the cell parameters of the crystalline structures. Additionally, a linear correlation is observed between experimental 23Na δiso values and calculated23Na σiso values from previously reported data and from our own measurements and calculations.

http://dx.doi.org/10.1021/jp3040727

Ionothermal 17O enrichment of oxides using microlitre quantities of labelled water

We present an ionothermal-based method for the simple and low-cost enrichment in 17O of oxide materials. This is demonstrated for the case of SIZ-4, an ionothermally-prepared aluminophosphate framework with the CHA topology. A preliminary study of unenriched samples of SIZ-4 highlights the importance of the careful choice of template in order to obtain an ordered structure. We then show how an ionothermal synthesis procedure incorporating microlitre quantities of 17O-enriched H2O enables as-prepared and calcined samples of SIZ-4 to be obtained with 17O enrichment levels that are sufficient to enable the recording of high-quality 17O solid-state NMR spectra. While second-order quadrupolar-broadened resonances are unresolved in 17O MAS NMR spectra, 17O double-rotation (DOR) and multiple-quantum (MQ)MAS NMR spectra reveal distinct resonances that are partially assigned by comparison with NMR parameters derived using first-principles calculations. The calculations also enable an investigation of the dependence of17O NMR parameters on the local structural environment. We find that both the17O isotropic chemical shift and quadrupolar coupling constant show clear dependencies on Al–O–P bond lengths, and angles and will therefore provide a sensitive probe of structure and geometry in aluminophosphate frameworks in future studies.

http://dx.doi.org/10.1039/C2SC20155K

The structure of fluoride-containing bioactive glasses: new insights from first-principles calculations and solid state NMR spectroscopy

Fluoride-containing bioactive glasses are attracting particular interest in many fields of dentistry and orthopedics because they combine the bone-bonding ability of bioactive glasses with the anticariogenic protection provided by fluoride ions. Since the biom, , edical applications of these materials critically depend on the release of ionic species in the surrounding physiological environment, a deep knowledge of their environments is required. In this paper, density functional theory calculations and spin effective Hamiltonians have been employed to analys, e the NMR signatures of the various environments of 19F, 29Si, 31P and 23Na atoms in fluorinated bioglasses structural models previously generated by Car–Parrinello molecular dynamics simulations. Comparison with experimental spectra expressly recorded in this work shows a good agreement and allows the enlightenment of some longstanding issues about the atomic structure of fluorinated bioglasses, such as the presence of Si–F and Si–O–P bonds. In particular, it is shown that Si–F bonds cannot be resolved by using MAS NMR experiments only, and 29Si{19F} REDOR experiments, that probes directly spatial proximities among atoms, must be employed. Our results show that F is coordinated entirely to the modifier ions Na and Ca, and that no Si–F bonds are present in the real glass structure. Thus, the addition of fluorine to the 45S5 Bioglass® increases the polymerization of the silicate network by removing modifiers from the siliceous matrix and reducing its reactivity. Finally, the computed isotropic chemical shifts of the various environments of phosphorus show that, if present, Si–O–P bonds should be clearly noticeable in the 31P static NMR experimental spectrum. Instead, the latter show that P is present as isolated orthophosphate units and does not enter into the siliceous matrix by forming Si–O–P bonds as conjectured by molecular dynamics simulations.

http://dx.doi.org/10.1039/C2JM30890H

CASTEP + DMol3

 

A Structural and Stability Evaluation of Au12 from an Isolated Cluster to the Deposited Material

The morphology and charged state of gold clusters play a crucial role in heterogeneous catalysis. The selection and optimization of theoretical approaches are necessary for the investigation of active sites on isolated and supported gold clusters. In the present paper, a study of the potential isomers of the Au12 cluster is performed within the DFT/PBE framework using a scalar-relativistic approach. We have found Au12 to be a dynamic cluster with at least 24 isomers due to the Jahn–Teller distortion. The majority of these isomers exhibit low symmetry, resulting in the formation of low-coordinated atoms, which are discussed in terms of frontier molecular orbitals and a Hirschfeld analysis of their atomic charges. The energy difference between the most energetically stable 2D (D3h) and 3D (C2v) isomers of Au12 is small (equal to 25 kJ/mol), which is evidence of their coexistence. The influence of the support on properties of the cluster is investigated using Au12/MgO(100). The 2D isomer of Au12 can interact with the surface either in an upright position, with two (Eads/atom = 24 kJ/mol) or three atoms (Eads/atom = 25 kJ/mol); the preferred position is planar (Eads/atom = 30 kJ/mol). The small deformation energy is required to distort a dynamic structure of Au12 compared to rigid gold clusters. The 3D isomer interacts with MgO(100) with two of its atoms (Eads/atom = 24 kJ/mol). The Au–Au distances across the surface increase, whereas the Au–Au distances at an angle to the surface are compressed with respect to the distances in the free clusters. The weak adsorption energies of Au12on MgO and the low activation barriers for gold atom migration (15 kJ/mol) between oxygen sites facilitate the diffusion of nanoparticles on the MgO surface.

http://dx.doi.org/10.1021/jp212367z

DMol3

 

Modeling Adsorption in Metal–Organic Frameworks with Open Metal Sites: Propane/Propylene Separations

We present a new approach for modeling adsorption in metal–organic frameworks (MOFs) with unsaturated metal centers and apply it to the challenging propane/propylene separation in copper(II) benzene-1,3,5-tricarboxylate (CuBTC). We obtain information about the specific interactions between olefins and the open metal sites of the MOF using quantum mechanical density functional theory. A proper consideration of all the relevant contributions to the adsorption energy enables us to extract the component that is due to specific attractive interactions between the π-orbitals of the alkene and the coordinatively unsaturated metal. This component is fitted using a combination of a Morse potential and a power law function and is then included into classical grand canonical Monte Carlo simulations of adsorption. Using this modified potential model, together with a standard Lennard-Jones model, we are able to predict the adsorption of not only propane (where no specific interactions are present), but also of propylene (where specific interactions are dominant). Binary adsorption isotherms for this mixture are in reasonable agreement with ideal adsorbed solution theory predictions. We compare our approach with previous attempts to predict adsorption in MOFs with open metal sites and suggest possible future routes for improving our model.

http://dx.doi.org/10.1021/la301215y

 

Structure and Stability of Hydrated β-MnO2 Surfaces

Hydration of the β-MnO2 (110), (100), and (101) surfaces is investigated using a combination of periodic density functional theory and ab initio thermodynamics. Fully hydrated surfaces are found to be significantly more stable than the stoichiometric ones up to temperatures in the range of 650 to 730 K at ambient oxygen and water partial pressures. A mixture of molecular and dissociative water adsorption is predicted to occur on the (110) and (101) surfaces, while the (100) surface does not dissociate water. Changes in surface reactivity upon water adsorption are explored via partial density of states analysis. Differences in surface relaxations and vibrational spectra are discussed and can be used to identify the type of adsorption mode.

http://dx.doi.org/10.1021/jp302268m

 

A first principles study of water adsorption on α-Pu (0 2 0) surface

Adsorptions of water in molecular (H2O) and dissociative (OH + H, H + O + H) configurations on the α-Pu (0 2 0) surface have been studied using ab initiomethods. The full-potential FP/LAPW + lo method has been used to calculate the adsorption energies at the scalar relativistic with no spin–orbit coupling (NSOC) and fully relativistic with spin–orbit coupling (SOC) theoretical levels. It is found that the SOC effect increases the adsorption energies by ∼0.30 eV for the two dissociative adsorptions. Weak physisorptions have been observed for the molecule H2O on theα-Pu (0 2 0) surface with primarily a covalent bonding, while the two dissociative adsorptions are chemisorptive with ionic bonding. The one-fold top site with an almost flat-lying orientation is found to be the most stable site for the adsorbed H2O molecule. At the SOC level, the most stable adsorption energy is 0.58 eV, the corresponding values being 5.44 eV and 5.73 eV for the partial dissociation and complete dissociation cases, respectively. The analysis of the local projected density of states shows that the surface Pu-5f electrons remain primarily chemically inert in the molecular water adsorption process. Completely dissociative adsorption at a long bridge site for the dissociated O atom and two short bridge sites for the two dissociated H atoms is the most stable adsorption site. Hybridizations of O(2p)–H(1s)–Pu(5f)–Pu(6d) are observed for the two dissociative adsorptions, implying that some of the Pu-5f electrons become further delocalized and participate in chemical bonding. Work functions decrease for the molecular and the partial adsorption processes while it increases for complete dissociation.

http://dx.doi.org/10.1016/j.jnucmat.2012.02.01

Theoretical study on the charge transport property of Pt(CNtBu)2(CN)2nanowires induced by Pt...Pt interactions

To deeply understand the charge-transporting nature of Pt(CNtBu)2(CN)2nanowires induced by intermolecular Pt...Pt interactions, calculations based on first-principle band structure and Marcus theory have been performed. The calculated bandwidths of the valence band, conducting band, and the effective masses of hole and electron are almost equal. This suggests that this complex has ambipolar transport characteristics, in agreement with experimental results. Density of states analysis revealed that the hole transport resulted mainly from the Pt...Pt interactions, while the electron transport was derived mainly from the CN groups. The character of the frontier molecular orbitals, reorganization energies and transfer integrals in different directions also supports the calculated first-principle band structure. Moreover, an investigation into the intermolecular interaction energy of neighbors revealed that there is a remarkable relationship between the intermolecular interaction energy and the transfer integral.

http://dx.doi.org/10.1039/C2DT00009A

GULP

 

Raman spectroscopy and lattice-dynamical calculations of Sc3CrO6 single crystals

Single crystals of Sc3CrO6 were grown by a high-temperature solution-growth method. They were studied using x-ray single-crystal diffractometry, scanning electron microscopy with x-ray microprobe analysis, and micro-Raman spectroscopy. The crystal structure was refined as a rhombohedral one with space group R3̅ , which confirms that it belongs to the Mg3TeO6-structural-type family. In the polarized Raman spectra collected at room temperature all 9Ag+9Eg Raman-allowed phonon modes were observed. The experimentally determined frequencies are compared to the results of lattice-dynamical calculations using a shell model. The Raman spectra, obtained with increasing temperature up to 600 C, do not provide direct indication for structural phase transition. The decrease with increasing temperature of the relative intensity of five Ag lines compared to the rest, however, suggests a possible structural phase transition from R3̅ to R3̅ c above the investigated temperature region.

http://dx.doi.org/10.1103/PhysRevB.85.214301

Chromia doped UO2 fuel: Investigation of the lattice parameter ß AREVA

Chromia doped UO2 fuel was characterised by electron microprobe analysis (EPMA) and X-ray powder diffraction (XRD). The macroscopic distribution of chromium across the fuel pellet (homogeneity, surface evaporation effect) and its microscopic state (extent of atomic scale dissolution in the UO2 matrix versus appearance as precipitates) was investigated. Furthermore, the lattice parameter obtained by X-ray powder diffraction was calculated by the unit cell refinement method and compared to empirical interatomic potential calculations (energy minimisation techniques). Finally, the theoretical density of the chromia doped fuel was calculated.

http://dx.doi.org/10.1016/j.jnucmat.2012.02.025