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                2012年3月-Materials Studio文献参考



                   First-principles calculations of structural, elastic and electronic properties of Nb2SnC under pressure
                   The structural, elastic and electronic properties of Nb2SnC under pressure were investigated by using first-principles plane-wave pseudo-potential density functional theory within the generalized gradient approximation (GGA). We find that the compressibility along the c-axis was lower than along the a-axis for pressures lower than 4 GPa, while the elastic constants, elastic modulus and the Debye temperature θD of Nb2SnC increase monotonically as the pressure increases. Finally, the density of states (DOS) at the Fermi level decreases with increasing pressure, due to the decrease of the contribution of Nb 4d states at the Fermi level.


                   First principle calculations for pressure induced structural phase transitions of Fe doped in SrMnO3
                   The pressure induced structural phase transition of Fe doped in SrMnO3 have been investigated using the pseudo-potential plane wave method within the generalized-gradient approximation plus on site repulsion U (GGA + U) method by first principles. The cooperative Jahn?Teller distortion is not found at zero pressure. By performing a structural phase stability analysis, the phase transition occurs between the cubic and tetragonal phase at 25.0 GPa. As pressure above 25.0 GPa, the different Mn?O and Fe?O bond lengths indicate that there is a strong Jahn?Teller distortion of the MnO6 and FeO6 octahedron, which is associate with structural transition. The Jahn?Teller distortion stabilizes a chain like antiferromagnetic (C-AFM) ground state. The band gap and density of states show that the electrical resistivity decreased as a result of the phase transition. The result gives an antiferromagnetic ground state for SrMn0.875Fe0.125O3 agreeing very well with the experimental report.


                   Iron reduction in nontronite-type clay minerals: Modelling a complex system
                   Reduction?oxidation or redox processes constitute a class of important reactions in a wide range of mineral environments. The specific focus in this investigation is on iron-bearing (ferruginous) clay minerals, where the redox reaction has important consequences for their structural and chemical integrity. Although this process has been studied experimentally, it is not yet fully understood where and how this occurs within clay mineral layers. The investigation presented here addresses this question from first principles using density functional theory (DFT), planewaves, pseudopotentials and periodic cells. The first issue addressed is that of simulating a dynamic reduction process using static models. Careful consideration is paid to the introduction of artificial electrostatic interactions, their subsequent identification and the effect these may have on the results. As a consequence of these considerations, three sets of models based on nontronite (Fe2(Si,Al)4O10(OH)2) are presented. The electronic structures of these clay mineral models are allowed to relax, to attain their own state of redox. By extensively analysing the Mulliken charges, magnetic states and orbital occupancy of iron, aluminium, silicon and oxygen, we have been able to draw firm conclusions about the relative reduction of iron within the tetrahedral and octahedral sheets of three varieties of nontronite. Reduction occurs to the greatest extent in the octahedral sheet iron and oxidation in the tetrahedral sheet iron. As these results reflect general, local environments within a clay mineral, they are therefore applicable to similar local environments and thus provide the foundations for further studies into more complex, geochemical systems.


                   The effects of Na on high pressure phases of CuIn0.5Ga0.5Se2 from ab initio calculation 
                   The effects of Na atoms on high pressure structural phase transitions of CuIn0.5Ga0.5Se2 (CIGS) were studied by an ab initio method using density functional theory. At ambient pressure, CIGS is known to have chalcopyrite (I-42d) structure. The high pressure phase transitions of CIGS were proposed to be the same as the order in the CuInSe2 phase transitions which are I-42d->Fm-3m->Cmcm structures. By using the mixture atoms method, the Na concentration in CIGS was studied at 0.1, 1.0 and 6.25%. The positive mixing enthalpy of Na at In/Ga sites (NaInGa) is higher than that of Na at Cu sites (NaCu). It confirmed previous studies that Na preferably substitutes on the Cu sites more than the (In, Ga) sites. From the energy?volume curves, we found that the effect of the Na substitutes is to reduce the hardness of CIGS under high pressure. The most significant effects occur at 6.25% Na. We also found that the electronic density of states of CIGS near the valence band maximum is increased noticeably in the chalcopyrite phase. The band gap is close in the cubic and orthorhombic phases. Also, the NaCu?Se bond length in the chalcopyrite phase is significantly reduced at 6.25% Na, compared with the pure Cu?Se bond length. Consequently, the energy band gap in this phase is wider than in pure CIGS, and the gap increased at the rate of 31 meV GPa?1 under pressure. The Na has a small effect on the transition pressure. The path of transformation from the cubic to orthorhombic phase was derived. The Cu?Se plane in the cubic phase displaced relatively parallel to the (In, Ga)?Se plane by 18% in order to transform to the Cmcm phase. The enthalpy barrier is 0.020 eV/atom, which is equivalent to a thermal energy of 248 K. We predicted that Fm-3m and Cmcm can coexist in some pressure range.


                   Electronic and optical properties of W-doped SnO2 from first-principles calculations
                   The electronic and optical properties of W-doped SnO2 are investigated by first-principles calculations in this work. The results show that the Fermi level shifts into the conduction band and the compound exhibits n-type metallic characters with high conductivity when W atoms substitute Sn atoms. As for defect cases, oxygen vacancies increase the density of states near the Fermi level resulting in a possible increase in the conductivity of W-doped SnO2, while the Sn vacancies make the Fermi level shift into the valence band and narrow the band gap. And the formation energy analysis indicates the possibility of W dopant and related defects forming in SnO2 crystal. The W-doped SnO2 shows high optical anisotropy, and the blue-shift of optical spectra can be observed. Additionally, the increased absorption in the visible region can be expected with the presence of oxygen vacancies in the crystal.


                   The structure, elastic, electronic properties and Debye temperature of M2AlC (M=V, Nb and Ta) under pressure from first-principles
                   With the help of first-principles generalized gradient approximation (GGA) calculation, the dependences of structure, elastic, electronic properties and Debye temperature of M2AlC (M V, Nb and Ta) ternary compounds on pressure were investigated based on density functional theory. Our calculated structural data are in good agreement with previous experiment and other theoretical results. It is shown that all the three compounds are mechanically stable. CM bonds are more resistant to deformation than the other bonds and the Nb2AlC is less resistant to deformation than V2AlC and Ta2AlC. The elastic properties including the isotropic bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν of the hexagonal M2AlC ternary compounds were determined using the Voigt?Reuss?Hill (VRH) averaging scheme. The results show that the shear modulus is the principal restraining factor for the stability of hexagonal M2AlC. The B/G and Poisson’s ratio under various pressures were also calculated. The band structure and density of states have been discussed, and the results indicate that with atomic number increasing, less valence electrons present in the unit cell, which leads to smaller values of Fermi level. The Debye temperatures ΘD of the M2AlC compounds were calculated from the elastic constants and sound velocities. It is indicated that pressure has little influence on the ΘD values.


                   Theory study of structural parameters, elastic stiffness, electronic structures and lattice dynamics of RBRh3 (R = Sc, Y, La and Lu)
                   Density functional-based method has been used to investigate the systematic trends for structural parameters, elastic stiffness, lattice dynamics and thermal properties of cubic perovskite-type RBRh3 depending on the type of R atoms (R are Sc, Y, La and Lu). The structural parameters, single-crystal elastic constants, directional elastic wave velocities and their pressure dependence are calculated and analyzed in comparison with the available experimental and theoretical data. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, Lamé’s coefficients, average sound velocity, Debye temperature and thermal conductivity are predicted in the frame work of the Voigt?Reuss?Hill approximation for the polycrystalline RBRh3. The correlation between the mechanical properties and electronic structures has been discussed. Using the density-functional perturbation theory (DFPT), the phonon properties of RBRh3 (R = Sc, Y and La) are investigated for the first time.


                   First principles calculations of hydrogen-induced decrease in the cohesive strength of α-Al2O3 single crystals
                   First principles calculations were conducted to investigate the effects of hydrogen on the cohesive strength of α-Al2O3 single crystals. The results show that the cohesive strength of α-Al2O3 single crystals decreases with increasing hydrogen concentration, CH. For example, the cohesive strength along the [0 0 1] direction, σth(0 0 1), decreases from 48.9 GPa (CH = 0) to 46.2 GPa (CH = 1630 wppm) and 39.6 GPa (CH = 4900 wppm). The lattice expansion and the changes in the local electronic structure caused by the hydrogen atoms are the two main reasons for the decrease in the cohesive strength. The results provide a computational evidence for the hydrogen-induced decrease in cohesive strength, which can explain the experimental phenomenon of hydrogen-assisted delayed fracture in α-Al2O3 ceramics during charging of hydrogen under a sustained load.



                   First-principles studies of structural, electronic and optical properties of AB2 (A = Si, Ge and B = O, S) Nanotubes
                   The structural, electronic and optical properties of AB2 (A = Si, Ge and B = O, S) nanotubes have been investigated by the first-principles calculations. The one-dimensional SiO2 nanotubes are predicted to be insulators with the large band gaps (?6 eV), while other tubes are semiconductors. The four types of nanotubes, especially for the SiS2-4 nanotube with a large absorption coefficient (?1.50 × 105 cm?1), generally exhibit strong absorption in UV region. The size dependences of optical properties on the tube-diameter are remarkable for SiO2, SiS2, and GeS2 nanotubes, while the absorption spectra in parallel (0 0 1) direction of GeO2 nanotubes are less sensitive to the radius of nanotube.


                   Influence of Ni and N on generalized stacking-fault energies in Fe?Cr?Ni alloy: A first principle study
                   The alloying effects of Ni and N were examined in terms of the generalized stacking-fault (SF) energy (GSFE). GSFE is associated with the basal plane of Fe?Cr?Ni austenitic stainless steel. The GSFE profiles were obtained using first-principle calculations. The results show that Ni increases the intrinsic SF energy γisf and the unstable SF energy γus. N does the opposite. However, a γisf/γus ratio close to zero accompanies the addition of Ni or N. This ratio implies that deformation by partial dislocation is preferred. Overall, the effect of N on Fe?Cr?Ni alloys is more evident than that of Ni.


                   First-principles calculation of compensated (2N, W) codoping impacts on band gap engineering in anatase TiO2
                   The electronic structures and optical properties of N-, W-, non-compensated (N, W) and compensated (2N, W) doped anatase TiO2 have been investigated using spin-polarized density functional theory. The calculated results demonstrate that compensated (2N, W) codoped TiO2 system not only gives rise to a much more effective band gap narrowing than non-compensated codoping and monodoping systems, but also forms the continuum states above the top of the valence band and eliminates the local energy states. We predict that compensated (2N, W) codoped TiO2 could serve as efficient visible-light photocatalyst.


                   Electrically tunable band gap in silicone
                   We report calculations of the electronic structure of silicene and the stability of its weakly buckled honeycomb lattice in an external electric field oriented perpendicular to the monolayer of Si atoms. The electric field produces a tunable band gap in the Dirac-type electronic spectrum, the gap being suppressed by a factor of about eight by the high polarizability of the system. At low electric fields, the interplay between this tunable band gap, which is specific to electrons on a honeycomb lattice, and the Kane-Mele spin-orbit coupling induces a transition from a topological to a band insulator, whereas at much higher electric fields silicene becomes a semimetal.


                   First-principles calculations of electronic, optical and elastic properties of Ba2MgWO6 double perovskite
                   The structural, electronic, optical and elastic properties of the cubic double perovskite Ba2MgWO6 were calculated using the ab initio plane wave method and compared with the available experimental data. The pressure effects were modeled by optimizing the crystal lattice structure and calculating the band gap at elevated hydrostatic pressures. The calculated values of the relative change of a unit cell volume with pressure are in excellent agreement with the recent experimental measurements [S. Meenakshi et al, J. Phys. Chem. Solids 72 (2011) 609]. The pressure coefficients of the lattice constant and the W-O, Mg-O, Ba-O bonds variations were all evaluated. Elastic anisotropic properties were analyzed by calculating all independent components of the elastic constants tensor; the greatest and the smallest values of the Young's moduli were determined.


                   On the electronic nature of silicon and germanium based oxynitrides and their related mechanical, optical and vibrational properties as obtained from DFT and DFPT
                   Electronic structure, bonding and optical properties of the orthorhombic oxynitrides Si2N2O and Ge2N2O are studied using the density function theory as implemented in pseudo-potential plane wave and full-potential (linearized) augmented plane wave plus local orbitals methods. Generalized gradient approximation is employed in order to determine the band gap energy. Indeed, the Si2N2O exhibits a large direct gap whereas Ge2N2O have an indirect one. Bonding is analyzed via the charge densities and Mulliken population, where the role of oxygen is investigated. The analysis of the elastic constants show the mechanical stability of both oxynitrides. Their bulk and shear modulus are slightly smaller than those reported on nitrides semiconductors due to the oxygen presence. The optical properties, namely the dielectric function, optical reflectivity, refractive index and electron energy loss, are reported for radiation up to 30 eV. The phonon dispersion relation, zone-center optical mode frequency, density of phonon states are calculated using the density functional perturbed theory. Thermodynamic properties of Si2N2O and Ge2N2O, such as heat capacity and Debye temperature, are given for reference. Our study suggests that Si2N2O and Ge2N2O could be a promising potential materials for applications in the microelectronics and optoelectronics areas of research.


                   Origin of the rigidity in tetragonal MB (M = Cr, Mo and W) and softening of defective WB: First-principles investigations
                   First-principles calculations were performed to understand the underlying origin of the rigidity of metal monoborides and effects of defects and impurities on the mechanical properties of tungsten mono-boride. A strong covalent bonding caused by a zig-zag structural topology is responsible for improving mechanical properties of monoborides. The occurrences of vacancies or impurities weaken the average bond strength, resulting in the mechanical properties degradation consequently, which demonstrated by electronic structure and charge density distributions.


                   Elastic properties, Debye temperature, density of states and electron?phonon coupling of ZrB12 under pressure
                   The structural para, , , , meters, elastic constants and the electronic density of states of ZrB12 under pressure are determined using first-principles calculations with plane-wave pseudopotential density functional theory, , within the generalized gradient approximation. From the elastic constants the elastic parameters and Debye temperature were calculated. They increase as the pressure is increased. The density of states at the Fermi level decrease, s as pressure is increased, changing from 0.576 to 0.515. Using the Debye temperature and the McMillan equation, the electron?phonon coupling constant was obtained as a function of pressure. It is found that the electron?phonon coupling constant is proportional to the logarithm of the ratio between the value of the Debye temperature and the value of the superconducting critical temperature.


                   Electronic Structure and Optical Properties of Antimony-Doped SnO2 from First-Principle Study
                   A first-principles study has been performed to calculate the electronic and optical properties of the SbxSn1?xO system. The simulations are based upon the method of generalized gradient approximations with the Perdew?Burke?Ernzerhof form in the framework of density functional theory. The supercell structure shows a trend from expanding to shrinking with the increasing Sb concentration. The increasing Sb concentration induces the band gap narrowing. Optical transition has shifted to the low energy range with increasing Sb concentration. Other important optical constants such as the dielectric function, reflectivity, refractive index, and electron energy loss function for Sb-doped SnO2 are discussed. The optical absorption edge of SnO2 doped with Sb also shows a redshift.


                   Manganese doped cadmium sulfide nanocrystal for hydrogen production from water under visible light
                   A series of Mn2+ doped CdS photocatalysts were prepared by a co-precipitation method and characterized by XRD, DRS, TEM, and XPS techniques. While the band gap, crystal phase and the morphology of CdS nanocrystal were not found to be affected noticeably by Mn2+ doping, there was an optimal Mn2+ doping content of wt 0.5% where the hydrogen production was more than doubled compared to pure CdS. Calculations of density functional theory (DFT) with plane waves and pseudopotentials were used to characterize the doping effect of Mn in cubic CdS. It is assumed that Mn2+ serving as shallow trapping sites can separate e?/h+ pairs at surface of nanosized CdS, so as to greatly reduce their surface recombination and which in turn leads to improved hydrogen yield.


                   Electrodeposition of Porous Mg(OH) 2 Thin Films Composed of Single-Crystal Nanosheets
                   Single-crystal nanosheets of magnesium hydroxide were electrodeposited from aqueous magnesium nitrate solution. SAED and in-situ dehydration study confirmed that the single-crystal Mg(OH)2 nanosheets were grown with their {011} planes for the first time. The average transmittance of the porous Mg(OH)2 films deposited at ?1.2 V over the visible region (390?780 nm) is 90.21%, which shows high optical transparency. The continuously growing nanosheets cross each other and join up, leading to the formation of continuous porous network of thin films.


                   CH4 dissociation on Co(0001): A density functional theory study
                   CH4 dissociation on Co(0001) surfaces is an important step, which has been investigated at the level of density functional theory. It is found that CH4 is unfavorable to adsorb on Co(0001), while CH4 favores to dissociate to CH3, CH2 and CH on Co(0001) surface by sequential dehydrogenation. In the whole process of CH4 dehydrogenation, CH4 dissociate to CH3 and H is the rate-determining step. The calculated results show that CH2 and CH exist mainly on Co(0001) surface, while the dehydrogenation of CH into C and H is difficult.


                CASTEP NMR

                   Benchmarks for the 13C NMR chemical shielding tensors in peptides in the solid state
                   The benchmark set is proposed, which comprises 126 principal elements of chemical shielding tensors, and the respective isotropic chemical shielding values, of all 42 13C nuclei in crystalline Tyr?D?Ala?Phe and Tyr?Ala?Phe tripeptides with known, but highly dissimilar structures. These data are obtained by both the NMR measurements and the density functional theory in the pseudopotential plane-wave scheme. Using the CASTEP program, several computational strategies are employed, for which the level of agreement between calculations and experiment is established. This set is mainly intended for the validation of methods capable of predicting the 13C NMR parameters in solid-state systems.


                CASTEP + Reflex

                   Preparation and XRD analyses of Na-doped ZnO nanorod arrays based on experiment and theory
                   ZnO nanorod arrays (NRAs) with different Na contents were prepared by thermal evaporation. Sodium pyrophosphate was adopted as the Na source. The Na contents in NRAs were determined by X-ray photoelectron spectra to be 0, 6.1, and 9.4 at.%. X-ray diffraction (XRD) analyses of Na-doped ZnO NRAs were performed in experiment and by first-principle calculation with the assumption of Na substitutions. A couple of typical changes were found in XRD patterns of Na-doped ZnO. The simulation results well agreed with the experimental data, which revealed that Na mainly located at the substitutional sites in Na-doped ZnO NRAs.


                CASTEP + DMol3 + Reflex

                   Study on the transformation from NaCl-type Na2TiO3to layered titanate
                   NaCl-type crystal structure sodium titanate (Na2TiO3), which exhibits a unit cell parameter of a=4.49 ?, was obtained by high temperature molten salt reaction. An intermediate phase product with layered structure was prepared by leaching the obtained Na2TiO3. We propose that the layered titanate structure is composed of Na2TiO3 and H2O, corresponding to the host-layer and guest-substance, respectively. Furthermore, the crystal structures of layered titanate were optimized by the density functional theory (DFT). This indicates that water molecules are distributed in an orderly manner in the interlayer through the formation of hydrogen-bonded chain. Moreover, the position of the adjacent lamella translates to c/2 along the c-axis after the intercalation of water.



                   Formaldehyde oxidation on the Pt/TiO2 (101) surface: A DFT investigation
                   Self-consistent periodic density function theory is employed to investigate formaldehyde (CH2O) oxidation by platinum supported on perfect anatase TiO2(101) surface in the presence of adsorbed oxygen or hydroxyl species. The adsorption structures and energies of all possible intermediates involved are investigated to map out the reaction network. Our results show that the primary intermediates, i.e., CH2O, CH2O2, CHO2, CHO, and CO2, prefer to adsorb at the Pt?5cTi bridge site, which is found as the most active site on Pt/TiO2, and formaldehyde directly dehydrogenates through the pathway of CH2O → CHO → CO, while the reaction pathway of CH2O → CH2O2 → CHO2 → CO2 is favorable in the presence of oxygen. In the latter process, the decomposition of formate is the rate-limiting step due to its relatively high decomposition barrier. Energy barrier decomposition analysis is used to elaborate the promotion effects resulting from the coadsorbed oxygen and hydroxyl on the C?H bond scission of CH2O and CH2O2. The theoretical work sheds new light on the title reactions and can serve as a theoretical approach to the catalysis mechanisms of metal oxide supporting transition metals with small organic molecules.


                   Chemically modified fullerene derivatives as photosensitizers in photodynamic therapy: A first-principles study
                   The first-principles density functional theory (DFT) and its time-dependent approach (TD-DFT) are used to characterize the electronic structures and optical spectra properties of five chemically modified fullerenes. It is revealed that the metal fullerene derivatives possess not only stronger absorption bands in visible light regions than organically modified fullerene but also the large energy gaps (ΔES?T > 0.98 eV) between the singlet ground state and the triplet state, which imply their significant aspect of potential candidates as a photosensitizer. We have found that a new metal-containing bisfullerene complexes (Pt(C60)2), with the extended conjugated π-electrons, much degenerate orbitals and a uniform electrostatic potential surface, behave more pre-eminent photosensitizing properties than other examined fullerene derivatives.


                   Interaction Energies and Spectroscopic Effects in the Adsorption of Formic Acid on Mineral Aerosol Surface Models
                   Heterogeneous reactions of atmospheric volatile organic compounds (VOCs) on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in airborne mineral dust in aerosols, and the atmospheric chemistry in general can be modified by their presence. In this work, the adsorption of a single formic acid molecule on different silicate surface models has been studied using quantum-mechanical methods. Both molecular clusters and a periodic crystal model of the (001) pyrophyllite surface have been employed, and all possible adsorption geometries have been considered. We find that silanol groups are always the most reactive formic acid adsorption sites. In the case of a periodic system, silanol groups at the crystal edges are favored. However, OH groups on the phyllosilicate octahedral sheet are also reactive sites through the tetrahedral cavities. The effect of formic acid adsorption on the spectroscopic properties of the whole system is also analyzed. Significant frequency shifts are detected in the vibration modes of both adsorbate and surface models. These results can be a useful tool for experimental adsorption investigations using vibration spectroscopy.


                   The synthesis and spectral properties of a stimuli-responsive D?π?A charge transfer dye based on indole donor and dicyanomethylene acceptor moiety
                   A dual mode chemosensor dye 3 for detection of fluoride ion, based on the D?π?A molecular framework by one-step condensation, presents high selectivity and sensitivity both in colorimetric and fluorometric analyses. Upon the addition of F? anion, the absorption band shows a remarkable red shift along with fluorescent intensity decreasing. The absorption and fluorescent intensities of the dye 3 can be reversibly selected by deprotonation/protonation of the amine moiety via control of intramolecular charge transfer (ICT), leading to a molecular switch with “on” and “off” states. 1H NMR titration analysis and DMol3 calculation were employed to reveal the intermolecular charge transfer system of dye 3?F? complex.


                   A combined nonequilibrium Green’s function/density-functional theory study of electrical conducting properties of artificial DNA duplexes
                   DNA duplexes have attracted much attention as a primary candidate for nanowires possessing self-organizing capability. To employ DNA duplexes as nanowires, however, a major drawback must be overcome; the guanine bases undergo oxidative degradation in a hole transport through DNA duplexes, which is likely caused by the presence of adjoining adenine bases that do not effectively mediate the charge transport through DNA duplexes. To overcome the drawback, several artificial nucleobases based on adenine have been designed and tested, confirming that the artificial nucleobase-containing DNA duplexes do not suffer from such an oxidative damage and exhibit high efficiency in hole transport through the DNA duplexes. In the present study, we examine the electrical conducting properties of these artificial DNA duplexes by use of nonequilibrium Green’s function and density-functional theory methods. The results explicate the origin of the experimentally observed high conductivity through the DNA duplexes containing the artificial DNA bases. We also put forth a computer-aided design of novel artificial DNA bases with low ionization energies, and examine the electrical conductivity of the DNA duplexes containing the designer nucleobases for potential use as highly conductive nanowires.


                   Interactions in different domains of truxenone supramolecular assembly on Au(111) 
                   The two-dimensional assemblies of truxenone, diindeno[1,2-a;1′,2′-c]fluorene-5,10,15-trione, on the Au(111) surface have been studied by scanning tunnelling microscopy in ultrahigh vacuum. It is found that the truxenone monolayer on Au(111) exhibits different two-dimensional supramolecular structures. The investigation using scanning tunnelling microscopy combined with the density functional theory calculations can be a helpful approach to understand the complicated supramolecular structures of truxenone self-assembly on Au(111).


                   An alternative approach: a highly selective dual responding fluoride sensor having active methylene group as binding site
                   A newly designed phosphonium derivative (L) having active methylene functionality, shows unusual preference towards F? over all other anions. The binding process through C?H...F? hydrogen bond formation was probed by monitoring the changes in either electronic or luminescence spectra. Changes in both cases are significant enough to allow visual detection. The loss of molecular flexibility of L on forming L?F? effectively interrupts the non-radiative deactivation pathway and accounts for the observed switch on fluorescence response. The results of the time-resolved emission studies for L and L?F? using a time-correlated single photon counting technique further corroborate this presumption. The excellent preference of L towards F? is attributed to an efficient hydrogen bonding interaction between the strongly polarized methylene protons and F?, which delineates the subtle difference in the affinity among other competing anionic analytes like CN?, H2PO4?, CH3CO2?, etc. The relative affinities of various anions and the preferential binding of F? to reagent L are also rationalized using computational studies.



                   Structure and catalytic properties of the most complex intergrown zeolite ITQ-39 determined by electron crystallography
                   Porous materials such as zeolites contain well-defined pores in molecular dimensions and have important industrial applications in catalysis, sorption and separation. Aluminosilicates with intersecting 10- and 12-ring channels are particularly interesting as selective catalysts. Many porous materials, especially zeolites, form only nanosized powders and some are intergrowths of different structures, making structure determination very challenging. Here, we report the atomic structures of an aluminosilicate zeolite family, ITQ-39, solved from nanocrystals only a few unit cells in size by electron crystallography. ITQ-39 is an intergrowth of three different polymorphs, built from the same layer but with different stacking sequences. ITQ-39 contains stacking faults and twinning with nano-sized domains, being the most complex zeolite ever solved. The unique structure of ITQ-39, with a three-dimensional intersecting pairwise 12-ring and 10-ring pore system, makes it a promising catalyst for converting naphtha into diesel fuel, a process of emerging interest for the petrochemical industry.


                   Spectroscopy study of SrAl2O4: Eu3+
                   Computational and experimental method is employed to study optical properties SrAl2O4 induced by europium dopant. Atomistic modeling is used to predict the doping sites and charge-compensation schemes for SrAl2O4:Eu systems and also to calculate the symmetry and the detailed geometry of the dopant site. This information is then used to calculate the crystal field parameters. SrAl2O4 doped with europium were prepared via a sol?gel proteic methodology. The photoluminescence experiments were performed at room temperature and at 13 K. The transition energy for the Eu3+-doped material is compared to the theoretical results. Based on Judd-Ofelt approach, the intensity parameters Ω2,4 of Eu3+ in the SrAl2O4 matrix were calculated.


                   Ab initio study of defect properties in YPO4
                   Ab initio methods based on density functional theory have been used to calculate the formation energies of intrinsic defects, including vacancies, interstitials, antisites and Frenkel pairs in YPO4 under the O-rich and Y2O3-rich, and the O-rich and Y-rich conditions. The larger size of the yttrium atom may give rise to higher formation energy of the phosphorus antisite defect. In general, the formation energies of anion interstitials are much smaller than those of cation interstitials for both conditions considered. It is of greatly interest to find that the relative stabilities among the same types of interstitials are independent of the reference states. The most stable configuration for oxygen interstitials is an O?O split interstitial near the Ta site, while the most stable configuration for cation interstitials is a tetrahedral interstitial near the Ta site. The cation split interstitials are unfavorable in YPO4, with much higher formation energies. Furthermore, the properties of Frenkel pairs are compared with those calculated using empirical potentials. The results reveal that both ab initio and empirical potential calculations show a similar trend in the formation energies of Frenkel pairs, but the formation energies obtained by empirical potentials are much larger than those calculated by ab initio method.


                   Improved Finnis?Sinclair potential for bcc vanadium solid
                   By introducing an exponential repulsion term to improve the repulsive interactions between the atoms, we refit the Finnis?Sinclair (FS) potential for bcc vanadium solid. The experimental cohesive energy, lattice constant and elastic constants of bcc vanadium solid are well reproduced. The agreement of calculated phonon dispersion and equation of state with experimental results further verify the good quality of our improved FS potential. The improved FS potential not only is able to give a better description of the fundamental properties of bcc vanadium solid, but also is suitable for simulation the structural damage due to neutron irritation in this material.


                   Molecular dynamics simulations of lattice thermal conductivity and spectral phonon mean free path of PbTe: Bulk and nanostructures
                   In this work, molecular dynamics (MD) simulations are performed to predict the lattice thermal conductivity of PbTe bulk and nanowires. The thermal conductivity of PbTe bulk is first studied in the temperature range 300?800 K. Excellent agreement with experiments is found in the entire temperature range when a small vacancy concentration is taken into consideration. By studying various configurations of vacancies, it is found that the thermal conductivity in PbTe bulk is more sensitive to the concentration rather than the type and distribution of vacancies. Spectral phonon relaxation times and mean free paths in PbTe bulk are obtained using the spectral energy density (SED) approach. It is revealed that the majority of thermal conductivity in PbTe is contributed by acoustic phonon modes with mean free paths below 100 nm. The spectral results at elevated temperatures indicate molecular scale feature sizes (less than 10 nm) are needed to achieve low thermal conductivity for PbTe. Simulations on PbTe nanowires with diameters up to 12 nm show moderate reduction in thermal conductivity as compared to bulk, depending on diameter, surface conditions and temperature.


                   Equilibrium and Growth Morphology of Oligoacenes: Periodic Bond Chains Analysis of Naphthalene, Anthracene, and Pentacene Crystals
                   The athermal equilibrium and growth crystal shapes of a series of oligoacenes, namely, naphthalene, anthracene, and pentacene, were simulated, in a vacuum, by using three different sets of empirical potentials (UNI, UFF, and MM3 force fields). By applying the Hartman?Perdok method of the periodic bond chains (PBC), the surface profiles were obtained, providing the specific surface and attachment energy values, both for ideal and relaxed surfaces. Very good agreement among the three force fields employed was observed. From calculations, it ensues that surface relaxation only weakly affects surface and, even more, attachment energies of these semiconductor molecular crystals. It is noteworthy to point out that both equilibrium and growth shapes of these crystals are quite similar when concerning phases belonging to the same point group.


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