2014年3月-Materials Studio文献参考

时间:2014-03-23

CASTEP

Density functional theory in the solid state ß review from CASTEP developers

Density functional theory (DFT) has been used in many fields of the physical sciences, but none so successfully as in the solid state. From its origins in condensed matter physics, it has expanded into materials science, high-pressure physics and mineralogy, solid-state chemistry and more, powering entire computational subdisciplines. Modern DFT simulation codes can calculate a vast range of structural, chemical, optical, spectroscopic, elastic, vibrational and thermodynamic phenomena. The ability to predict structure–property relationships has revolutionized experimental fields, such as vibrational and solid-state NMR spectroscopy, where it is the primary method to analyse and interpret experimental spectra. In semiconductor physics, great progress has been made in the electronic structure of bulk and defect states despite the severe challenges presented by the description of excited states. Studies are no longer restricted to known crystallographic structures. DFT is increasingly used as an exploratory tool for materials discovery and computational experiments, culminating in ex nihilo crystal structure prediction, which addresses the long-standing difficult problem of how to predict crystal structure polymorphs from nothing but a specified chemical composition. We present an overview of the capabilities of solid-state DFT simulations in all of these topics, illustrated with recent examples using the CASTEP computer program.

http://dx.doi.org/10.1098/rsta.2013.0270

DNA-based nanobiostructured devices: The role of quasiperiodicity and correlation effects

The purpose of this review is to present a comprehensive and up-to-date account of the main physical properties of DNA-based nanobiostructured devices, stressing the role played by their quasi-periodicity arrangement and correlation effects. Although the DNA-like molecule is usually described as a short-ranged correlated random ladder, artificial segments can be grown following quasiperiodic sequences as, for instance, the Fibonacci and Rudin–Shapiro ones. They have interesting properties like a complex fractal spectra of energy, which can be considered as their indelible mark, and collective properties that are not shared by their constituents. These collective properties are due to the presence of long-range correlations, which are expected to be reflected somehow in their various spectra (electronic transmission, density of states, etc.) defining another description of disorder. Although long-range correlations are responsible for the effective electronic transport at specific resonant energies of finite DNA segments, much of the anomalous spread of an initially localized electron wave-packet can be accounted by short-range pair correlations, suggesting that an approach based on the inclusion of further short-range correlations on the nucleotide distribution leads to an adequate description of the electronic properties of DNA segments. The introduction of defects may generate states within the gap, and substantially improves the conductance, specially of finite branches. They usually become exponentially localized for any amount of disorder, and have the property to tailor the electronic transport properties of DNA-based nanoelectronic devices. In particular, symmetric and antisymmetric correlations have quite distinct influence on the nature of the electronic states, and a diluted distribution of defects lead to an anomalous diffusion of the electronic wave-packet. Nonlinear contributions, arising from the coupling between electrons and the molecular vibrations, promote an electronic self-trapping, thus opening up the possibility of controlling the spreading of the electronic density by an external field. The main features of DNA-based nanobiostructured devices presented in this review will include their electronic density of states, energy profiles, thermodynamic properties, localization, correlation effects, scale laws, fractal and multifractal analysis, and anhydrous crystals of their bases, among others. New features, like other nanobiostructured devices, as well as the future directions in this field are also presented and discussed.

http://dx.doi.org/10.1016/j.physrep.2013.10.004

 

Electron-Phonon Coupling and the Metallization of Solid Helium at Terapascal Pressures

Solid He is studied in the pressure and temperature ranges 1–40 TPa and 0–10 000 K using first-principles methods. Anharmonic vibrational properties are calculated within a self-consistent field framework, including the internal and free energies, density-pressure relation, stress tensor, thermal expansion, and the electron-phonon coupling renormalization of the electronic band gap. We find that an accurate description of electron-phonon coupling requires us to use a nonperturbative approach. The metallization pressure of 32.9 TPa at 0 K is larger than found previously. The vibrational effects are large; for example, at P=30  TPa the band gap is increased by 2.8 eV by electron-phonon coupling and a further 0.1 eV by thermal expansion compared to the static value. The implications of the calculated metallization pressure for the cooling of white dwarfs are discussed.

http://dx.doi.org/10.1103/PhysRevLett.112.055504

 

First-principles study of ceramic material (Ti1xNbx)2AlC compounds and its compressive behavior under pressure up to 55 GPa

The structural, elastic, mechanical, electronic properties and its compressive behavior up to 55 GPa are studied for the (Ti1xNbx)2AlC (x = 0, 0.25, 0.5, 0.75, 1.0) compounds using the first-principles calculation. Calculated structural parameters are in good agreement with experimental results, and all the considered (Ti1xNbx)2AlC compounds are predicted to be elastically stable under 0–55 GPa pressure and are classified as brittle materials. Meanwhile, our study provides a metallic character of all the considered (Ti1xNbx)2AlC compounds, and predicts them as promising good coating materials. Moreover, a significant increase (25.8%) in the bulk modulus is found with the Nb concentration changing from 0 to 1.0, and the reason is analyzed.

http://dx.doi.org/10.1016/j.jallcom.2013.12.233

 

The effect of Ce-N codoping on the electronic structure and optical property of anatase TiO2: A first-principles study

Based on the first-principles plane wave ultra-soft pseudo potential (USP) method of density function theory pure N and Ce doped and Ce–N codoping anatase TiO2 supercell models were established, respectively, and calculated their energy in this paper. The calculated results show that the three doping systems compared to the pure anatase TiO2 band gap narrowed which results in red-shift of the optical absorption edges and Ce–N codoped anatase TiO2 have the most obvious visible effect. Meanwhile, synergy is very effective for the separation of electron–hole pairs and the electrons have a better lifespan. Research found that the trend of the donor's movements at the shallow level of Ce–N codoped anatase TiO2 is not obvious. This is due to its very thick shell, resulting in shielding effect of the outer layer of the Ce-4f.

http://dx.doi.org/10.1142/S0217979214500453

 

First-principles study of the structural, electronic and elastic properties of ternary Zr2AN (A = Ga, In and Tl)

The structural, electronic and elastic properties of ternary Zr2AN (A = Ga, In and Tl) ceramics have been studied by first-principles calculations. The obtained lattice parameters are in agreement with available data. The computed lattice parameters increase with increasing the atomic radii for A elements, whereas the cohesive energies and Debye temperatures decrease accordingly. The band structure shows that these three ceramics are all conductive. The density of states at the Fermi level (Ef) mainly originates from Zr dstate with a minor contribution of A p states. Below Ef, the hybridization peak of Zr d–N p lies in lower energy range which indicates that Zr–N bond is stronger than Zr–A bond. The charge density distribution shows that Zr and N atoms form a strong Zr–N–Zr covalently bonded chain.

http://dx.doi.org/10.1016/j.commatsci.2013.11.040

 

The electronic structure and phase diagram of chlorine adsorption on Mg (0 0 0 1) surface

First-principles methods are applied to investigate the adsorption energy and electronic structure of p(2 × 2) configuration of chlorine atoms adsorbed in variety of sites of Mg (0 0 0 1) surface. It is found that the fcc-hollow site is the energetically most favorable for the whole coverage range considered. The adsorption energy decreases with the increasing coverage θ. It can be concluded from the charge densities and density of states that the charges transfer between substrate Mg atoms and Cl atoms leads to the appearance of dipole moment. It has been also found from the electronic structure that the repulsion between Cl atoms becomes stronger and the charge distribution is localized getting closer to the Cl atoms with the increasing coverage. The chlorine adatom reduces the surface energy rapidly and leads to form the stable bulk MgCl2and in the fcc-hollow site adsorption the 1/4 ML Cl–Mg structure is stable while the higher 1/2 ML, 3/4ML and 1/1ML Cl–Mg structures are unstable from the phase diagram of Cl–Mg structures.

http://dx.doi.org/10.1016/j.commatsci.2013.11.064

 

Half-metallic ferromagnetism in zinc-blende (CaX)1/(YX)1 (0 0 1)(Y = Al, Ga, and In; X = N, P, and As) superlattices: A first-principles study

Using first-principles calculation based on density functional theory, the electronic and magnetic properties of zinc-blende (CaX)1/(YX)1 (Y = Al, Ga, and In; X = N, P, and As) superlattices in the (0 0 1) direction are investigated. Results show that all these nine superlattices are half-metals with a total magnetic moment of 1 μB. The ferromagnetism comes essentially from the p orbitals of the N, P, and As anions. Moreover, the large half-metallic gaps, the robust stability of the half-metallicity with respect to the lattice contraction, and the small mismatch of lattice constants between the predicted half-metallic superlattices and some corresponding zinc-blende semiconductors make them promising candidates for successful spintronics applications.

http://dx.doi.org/10.1016/j.commatsci.2013.12.031

 

First-principles study of the structural, electronic and optical properties of tetragonal LiIO3

The structural parameters, electronic structure, chemical bonding, and optical properties of tetragonal LiIO3 have been studied using the ab initio   pseudopotential density functional method within the generalized gradient approximation. The structural parameters of tetragonal LiIO3 agree well with the experimental data. Results are given for bulk modulus B   and its pressure derivative View the MathML source. The energy band structure, density of states, and Mulliken charge population are obtained, which indicates that tetragonal LiIO3 has an indirect band gap of 2.65 eV at AΓ, in the absence of the scissors operation. Furthermore, in order to clarify the mechanism of optical transitions of tetragonal LiIO3, the complex dielectric function ε(ω), refractive indexn(ω), extinction coefficient κ(ω), absorption efficient α(ω), reflectivity R(ω) and energy loss function L(ω) are also calculated.

http://dx.doi.org/10.1016/j.commatsci.2013.12.025

 

Interface structure of Nb films on single crystal MgO(1 0 0) and MgO(1 1 1) substrates

This study systematically investigates the interface structure of Nb films grown on MgO substrates with different orientations ((1 0 0) and (1 1 1)) by experiments and simulations. X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to characterize the structure of Nb films and the structure of interfaces between Nb films and MgO substrates. The results show that thin films exhibit different preferred planes on different orientations of MgO substrates. First-principles calculations were used to understand the interface configuration through a coherent interface model. The combination of experiments and simulations shows that the work of separation, together with substrate orientation and lattice mismatch, determines the interface structure between films and substrates.

http://dx.doi.org/10.1016/j.actamat.2013.11.031

 

Research on electronic structure and optical properties of Mg doped Ga0.75Al0.25N

In order to study the influence of Mg doping on the electronic structure and optical properties of wurtzite Ga0.75Al0.25N and the hydrogen passivation of Mg-doped Ga0.75Al0.25N, models of Ga0.6875Mg0.0625Al0.25N, Ga0.75Mg0.0625Al0.1875N and Ga0.6875(MgH)0.0625Al0.25N are built. Based on first principle calculation, the atomic structures, band structure, Mulliken population, and optical properties of the Mg doped and Mg–H co-doped crystals are obtained. Results show the formation energy of Mg–H complex is smaller than that of only Mg doping in the material. The Fermi levels of the two Mg doped crystals enter into the valence bands and Mg doping makes the crystals turn into p-type degeneracy semiconductors. Meanwhile, the Fermi level goes back to the gap between conduction band and valence band in the Mg–H codoped model. The Mulliken charge of Mg atom decreases after adding the H atom, showing that hydrogen results in the passivation and weaker ionicity of the Mg impurity. After Mg doping, the first dielectric peak shifts to lower energy since the Al:3p and Ga:4p state in the conduction band move to the range of lower energy. The metal reflective region of the semiconductor also shift to lower energy range after My doping. Mg doping enhances the absorption coefficient at the range of 1.05–3.47 eV while weakens it at the range of the 10.00–20.00 eV.

http://dx.doi.org/10.1016/j.optmat.2013.11.028

 

The optical properties of NiAs phase ZnO under pressure calculated by GGA+U method

To comprehend the optical properties of the recent-predicted NiAs phase ZnO under pressure, we used the generalized gradient approximation plus U (GGA+U) method to calculate the properties. The GGA+U method is more suited for the strong correlated NiAs phase. The direct band gap increases with increasing pressure. The calculated band gap shows that NiAs phase is an insulator, while the real part ε1(ω) shows the NiAs phase expresses metallic behavior around 18.6 (22.5 GPa) and 26.0 eV (215 GPa). The relation between the imaginary part ε2(ω) and PDOS was also discussed. The calculated optical constants show the NiAs phase is transparent and can be used in the vacuum ultraviolet region. We also compared the optical constants of NiAs with wurtzite and CsCl phases ZnO at according transition pressure. And the new-appeared peaks of optical constants can be used to identify the phase transition. The blue-shift optical constants of NiAs phase ZnO can be used to measure pressure after carefully calibrated. Our research provides a reference for identifying and using the NiAs phase ZnO under pressure.

http://dx.doi.org/10.1016/j.optcom.2013.09.035

 

First-principles calculations of water dissociation on the oxygen-deficient (010) surface of Fergusonite-type LaNbO4 crystal

The water-containing atmosphere plays an important role in the improvement of proton conductivity of LaNbO4. The interaction between the water molecule and the oxygen-deficient (010) surface of LaNbO4crystal has been investigated via first-principles calculations. The water molecule is set at different heights over the oxygen vacancy and the exposed niobium atom in Nb–O tetrahedron. The adsorption and dissociation behavior of the water molecule to the surface are illustrated and analyzed by the total and localized density of states (DOS) plots. By finely adjusting the heights of the water molecule from the surface, the relatively stable position for the water molecule is determined by free energies of the hydrated slabs. The water molecule prefers to adsorb onto LaNbO4 (010) surface and then to dissociate into one proton and one hydroxyl over the oxygen vacancy rather than over the exposed niobium atom in Nb–O tetrahedron.

http://dx.doi.org/10.1016/j.ijhydene.2013.11.018

 

Interaction of hydrogen and carbon dioxide with sod-type zeolitic imidazolate frameworks: a periodic DFT-D study

Dispersion-corrected density-functional theory (DFT-D) calculations are used to study the interaction of hydrogen and carbon dioxide with ZIF-8, a prototypical zeolitic imidazolate framework (ZIF) with sodalite topology. Four distinct adsorption sites are identified for each of the two guest species. Two of the sites are associated with the six-ring windows, a third site is located close to one imidazolate moiety, and the fourth site is situated in the close proximity of two methyl substituents of the methylimidazolate linkers. For the case of hydrogen, where experimental data are available, the positions and the energetic ordering obtained in the DFT-D calculations agree well with these data. The investigation is then extended to two groups of isostructural systems. The first group consists of two boron imidazolate frameworks (BIFs), in which the tetrahedrally coordinated atoms (T atoms) differ from those in ZIF-8, while the methylimidazolate linker remains the same. The calculations show that the nature of the T atoms has only a very limited effect on the interaction with the guest molecules. The second group of derivatives comprises four systems that incorporate the same T atom as ZIF-8 (zinc), but linkers with different substituents X, with X = –H, –NO2, –NH2, –CHO. In these cases, the interaction with CO2 and, to a much lesser extent, hydrogen is increased at the adsorption site that is associated with the substituents, most prominently in the nitro- and aldehyde-functionalised systems. A detailed analysis of the adsorption geometries is used to explain the favourable effect of the substituents. Furthermore, it is shown how a reasonable estimate of the average interaction energy can be obtained from a weighted average over the different adsorption sites, accounting for their possible occupancy. In the case of ZIF-8, this averaged value is compared to experimental heats of adsorption, and the deviations are discussed. Finally, possible applications in hydrogen storage and CO2/H2 separation are discussed. All materials show similar affinities for hydrogen, indicating that their performance in H2 storage applications is largely independent of the structural modifications considered. Because the CO2/H2 selectivity is related to the difference in affinity towards the two species, it can be expected from the DFT-D results that the nitro- and aldehyde-functionalised systems will perform considerably better than ZIF-8, especially for the removal of relatively small amounts of carbon dioxide from a hydrogen feed. This finding is particularly encouraging as both systems are synthetically accessible.

http://dx.doi.org/10.1039/C3CE42209G

 

Doping potassium ions in silver cyanide complexes for green luminescence

Doping potassium ions in silver cyanide complexes leads to two heterometallic silver–potassium cyanide complexes, namely, [Me4N]2[KAg3(CN)6] (1) with a typical NaCl-type framework containing distinct ligand-unsupported argentophilic interactions, and [Ag3(H2O)3][K(CN)2]3 (2) with an unprecedented 3-D (4,4,6,6)-connected framework formed by unique [Ag3(H2O)3] clusters connecting concave–convex 2[K(CN)2] layers. The two complexes exhibit green luminescence, and the relationships between their structures and photoluminescence, as well as the regulating effect on the luminescence by doping of potassium ions are well investigated via density functional theory analysis.

http://dx.doi.org/10.1039/C3DT53219D

 

Ab Initio Calculations of the Structural and Electronic Properties of Ca2La3Sb3O14 Weberite at Ambient and Elevated Hydrostatic Pressure

The structural and electronic properties of the Ca2La3Sb3O14 were calculated for the first time using the density functional theory (DFT) methods. The material crystallizes in the weberite structure. The optimized crystal structure constants are in good agreement with the experimental findings. The calculated direct bandgap was 1.864 eV (in the generalized gradient approximation) and 2.443 eV (in the local density approximation). The bulk modulus values obtained from the pressure dependence of the optimized unit cell volume were 128.72 GPa (GGA) and 158.56 GPa (LDA), respectively. Influence of the hydrostatic pressure on the structural and electronic properties was also examined in in this work.

http://dx.doi.org/10.1149/2.002402jss

 

Raman scattering in orthorhombic CuInS2  nanocrystals

We report the results of non-resonant and resonant Raman scattering in orthorhombic nanocrystalline CuInS2 semiconductor, supported by density functional first principle lattice dynamics calculations. A larger number of dominant phonon modes in comparison with standard tetragonal CuInS2 phases is shown to be associated with peculiarities of cation sublattice ordering and is the “fingerprint” of the corresponding structural polymorph. Good overall agreement is found between theoretical and experimental phonon mode frequencies.

http://dx.doi.org/10.1002/pssa.201330229

 

Mechanism study on Raney nickel-catalyzed amination of resorcinol

Amination of resorcinol catalyzed by Raney nickel has been examined with good yield. Using the first principle density functional theory, some detailed mechanism of the amination of resorcinol on the Ni(111) surface is explored. The resorcinol is adsorbed on the Ni surface at the hollow site to form ketone by isomerization. The isomerization has a barrier of 122.1 kJ/mol. Ketone can couple with secondary amine mediated by resorcinol to afford hemiaminal. For the formation of hemiaminal, the steric effect of the alkyl group of secondary amine is obvious. Hemiaminal undergoes dehydration to get final product, which occurs by the preferred adsorption in the bridge site, cleavage of Csingle bondO bond initially, followed by subsequent cleavage of Csingle bondH bond.

http://dx.doi.org/10.1016/j.catcom.2013.12.021

 

DMol3

 

Structure of Mo2Cx  and Mo4Cx  Molybdenum Carbide Nanoparticles and Their Anchoring Sites on ZSM-5 Zeolites ß Jason DeJoannis (and GXF)

Mo carbide nanoparticles supported on ZSM-5 zeolites are promising catalysts for methane dehydroaromatization. For this and other applications, it is important to identify the structure and anchoring sites of Mo carbide nanoparticles. In this work, structures of Mo2Cx(x = 1, 2, 3, 4, and 6) and Mo4Cx (x = 2, 4, 6, and 8) nanoparticles are identified using a genetic algorithm with density functional theory (DFT) calculations. The ZSM-5 anchoring sites are determined by evaluating infrared vibrational spectra for surface OH groups before and after Mo deposition. The spectroscopic results demonstrate that initial Mo oxide species preferentially anchors on framework Al sites and partially on Si sites on the external surface of the zeolite. In addition, Mo oxide deposition causes some dealumination, and a small fraction of Mo oxide species anchor on extraframework Al sites. Anchoring modes of Mo carbide nanoparticles are evaluated with DFT cluster calculations and with hybrid quantum mechanical and molecular mechanical (QM/MM) periodic structure calculations. Calculation results suggest that binding through two Mo atoms is energetically preferable for all Mo carbide nanoparticles on double Al-atom framework sites and external Si sites. On single Al-atom framework sites, the preferential binding mode depends on the particle composition. The calculations also suggest that Mo carbide nanoparticles with a C/Mo ratio greater than 1.5 are more stable on external Si sites and, thus, likely to migrate from zeolite pores onto the external surface of the zeolite. Therefore, in order to minimize such migration, the C/Mo ratio for zeolite-supported Mo carbide nanoparticles under hydrocarbon reaction conditions should be maintained below 1.5.

http://dx.doi.org/10.1021/jp4106053

 

A priori prediction of the octanol–water partition coefficient (Kow) of ionic liquids ß COSMO-SAC + DMol3 in Cerius2

The octanol–water partition coefficient (Kow) of ionic liquids (ILs) is an important indicator for its toxicity and environment impact. In this work, the Kow is determined from the ratio of infinite dilution activity coefficient of IL in the water-rich and octanol-rich phases. In particular, the Pitzer-Debye−Hückel (PDH) model combined with the predictive COSMO-SAC model is used for calculating the activity coefficients. A root-mean square deviation of 0.75 is achieved for log Kow, or a factor of 4 in Kow, for a total of 67 ILs at ambient condition. The long-range coulomb interactions (from the DH model) contribute an almost constant value of −1.35 to logKow, regardless of the type of IL. The change of log Kow with the molecular structure of IL is found to be dominated by the short-range attractive interactions between the IL and the solvents, including the hydrogen bonding and nonhydrogen bonding surface interactions. The combination of PDH and COSMO-SAC models provides not only the quantitative predictions of Kow of ILs and but also physical insights to the relations between Kow and the molecular structure of ILs.

http://dx.doi.org/10.1016/j.fluid.2013.11.042

 

Synthesis of new acenaphtho[1,2-c]thiophene-based low bandgap polymers for organic photovoltaics

Donor–acceptor conjugated polymers, PDTTPDA and PDTTPDT, composed of new acenaphtho[1,2-c]thiophene or thiophene as electron donors and 1,3-dithien-2-yl-thieno[3,4-c]pyrrole-4,6-dione (DTTPD) as the electron acceptor were synthesized by a Stille cross-coupling reaction. These polymers combine interesting properties such as good solubility and excellent thermal stability. The weight-averaged molecular weights (Mw) of PDTTPDA and PDTTPDT were found to be 71,000 and 79,000 with polydispersity indices of 1.65 and 1.66, respectively. Photophysical studies revealed a low bandgap of 1.77 eV for PDTTPDA and 1.72 eV for PDTTPDT. The present study indicates that the combination of DTTPD and acenaphtho[1,2-c]thiophene building blocks can be a very effective way to lower the HOMO energy level and ultimately to enhance the Voc of polymer solar cells. The Voc reported here (up to 0.94 V) is one of the highest observed in polymer:PCBM bulk heterojunction devices, and a power conversion efficiency (PCE) of up to 3.28% was observed in the PDTTPDA devices.

http://dx.doi.org/10.1016/j.solmat.2013.12.016

 

Synthesis, structure and theoretical investigation into a homoleptic tris(dithiolene) tungsten

A new homoleptic dithiolene tungsten complex, tris-{1,2-bis(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S′}tungsten, was successfully synthesized via a reaction of the thiophosphate ester and sodium tungstate. The thiophosphate ester was prepared from 3,5-dimethoxybenzaldehyde via benzoin condensation to produce the intermediate 1,2-bis-(3,5-dimethoxyphenyl)-2-hydroxy-ethanone compound, followed by a reaction of the intermediate with phosphorus pentasulfide. FTIR, UV–Vis spectroscopy, 1H NMR and 13C NMR and elemental analysis confirmed the product as tris{1,2-bis-(3,5-dimethoxyphenyl)-1,2-ethylenodithiolene-S,S′}tungsten with the molecular formula of C54H54O12S6W. Crystals of the product adopted a monoclinic system with space group of P2(1)/n, where a = 12.756(2) Å, b = 21.560(3) Å,c = 24.980(4) Å and β = 103.998(3)°. Three thioester ligands were attached to the tungsten as bidentate chelates to form a distorted octahedral geometry. Density functional theory calculations were performed to investigate the molecular properties in a generalized-gradient approximation framework system using Perdew–Burke–Ernzerhof functions and a double numeric plus polarization basis set. The HOMO was concentrated on the phenyl ligands, while the LUMO was found along the W(S2C2)3 rings. The theoretical optical properties showed a slight blue shift in several low dielectric solvents. The solvatochromism effect was insignificant for high polar solvents.

http://dx.doi.org/10.1016/j.saa.2013.09.069

 

Comparative studies and modeling structures of two new isomers containing binuclear PdII complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ)

The synthesis and comparative studies of two new binuclear PdII isomer complexes derived from TPTZ, [2,4,6-tri-(2-pyridyl)-1,3,5-triazine], have been synthesized and characterized. Their structures have been investigated by elemental analyses, spectral (IR, UV–vis, mass and 1H-NMR) and thermal measurements. Electronic and magnetic studies suggest a distorted square-planar around the two PdII ions. The HOMO, LUMO and DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and their complexes. Kinetic parameters were determined using Coats–Redfern and Horowitz–Metzger methods. Also, the geometry of the two isomers is confirmed using DFT method from DMOL3 calculations. Moreover, the two PdII complexes have different specific optical rotation where the red PdII complex has dextrorotatory (+5.68) while the yellow PdII complex has levorotatory (−9.37). The results of biological activity for the two PdII complexes promised to be effective in tumor treatment.

http://dx.doi.org/10.1016/j.saa.2013.10.118

 

Carbon Nanotubes and Activated Carbons Supported Catalysts for Phenol in Situ Hydrogenation: Hydrophobic/Hydrophilic Effect

Carbon nanotube (CNTs) and activated carbon (AC) supported Pd and Ni catalysts were prepared for the (in situ) hydrogenation of phenol to cyclohexanone and cyclohexanol. The hydrophobic/hydrophilic properties of the catalysts were tailored by pretreating the carbonaceous support with HNO3 at various conditions and characterized by X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and transmission electron microscopy (TEM). The catalytic results suggested that Pd and Ni supported on CNTs show significantly higher activity than that supported on ACs. Pretreating the CNTs with HNO3 increases the local hydrophilicity of the active phase (by introducing oxygenated groups), which result in an increase in the cyclohexanone selectivity and strongly decrease the phenol conversion. The first-principles density functional theory calculation suggested that the adsorption/desorption behaviors of phenol, methanol, H2O, and cyclohexanone on the catalysts might be influenced highly by the hydrophobic/hydrophilic properties. The hydrophilic catalysts show high selectivity in cyclohexanone by lower conversion in phenol or vice versa.

http://dx.doi.org/10.1021/ie4035253

 

A theoretical study of Cu clusters in siliceous erionite

In terms of periodic density functional theory method, we present a theoretical study of the structure and electronic properties of different composites, obtained by the inclusion of distinct Cux (x=2,4,6,8) clusters within the C1 cage of siliceous erionite–zeolite. Results shows that for a periodic distribution of Cux clusters on zeolite, the hosting of those is trough electrostatic confinement which is governed by framework oxygen atoms located at particular equivalent sites. However, when the permanency of a cluster in a C1cage is compromised, the cluster–cluster long range Coulomb interactions could rise to keep it inside. In addition, results also show that the electronic properties of free Cux clusters are largely transferred to the formed composite.

http://dx.doi.org/10.1016/j.molstruc.2013.09.019

 

Computational screening of several silicon-based high-energy hexanitrohexaazaisowurtzitane-like derivatives

Silicon-based hexanitrohexaazaisowurtzitane (CL-20) derivatives, including nitro (single bondNO2) and difluoramino (single bondNF2) group containing derivatives, may become important high-energy compounds. Density Functional Theory Becke exchange plus Perdew correlation (BP) with triple numerical set plus polarization functions (TNP) and homodesmotic reactions were employed to calculate cage strain energies, gaseous phase formation enthalpies of several silicon-based CL-20 derivatives. Comparative studies were carried out between silicon-based CL-20 nitro and difluoramine derivatives. The structural stability of these silicon-based CL-20 derivatives were evaluated in terms of Nsingle bondNO2 or Nsingle bondNF2 bond dissociation energies and Mulliken charges of single bondNO2 or single bondNF2 groups by means of density functional theory revised versions of the Perdew–Burke–Ernzerhof (RPBE) with TNP functions, and the exchange component of Perdew and Wang's 1991 functional (PW91) with TNP functions, two theoretical methods were chosen according to experimental data. The theoretical studies show that their performances are better than CL-20 in terms of detonation velocities, detonation pressures and explosion temperatures. Structural stability of these silicon-based CL-20 derivatives is higher than CL-20 according to Nsingle bondNO2 or Nsingle bondNF2 bond dissociation energies and cage strain energies. This work will lay some foundations for the future explorations of novel high-energy silicon-based compounds.

http://dx.doi.org/10.1016/j.jfluchem.2013.12.001

 

Insights into the reaction mechanisms of methanol decomposition, methanol oxidation and steam reforming of methanol on Cu(111): A density functional theory study

Cu-based catalysts have been widely used for hydrogen production from methanol decomposition, methanol oxidation and steam reforming of methanol (MSR). In this study, we have systematically identified possible reaction paths for the thermodynamics and dynamics involved in the three reactions on a Cu(111) surface at the molecular level. We find that the reaction paths of the three reactions are the same at the beginning, where methanol scission is favourable involving O–H bond scission followed by sequential dehydrogenation to formaldehyde. Formaldehyde is an important intermediate in the three reactions, where direct dehydrogenation of formaldehyde to CO is favourable for methanol decomposition; for methanol oxidation, formaldehyde tends to react with oxygen to form dioxymethylene through C–H bond breaking and finally the end products are mainly CO2 and hydrogen; for MSR, formaldehyde tends to react with hydroxyl to form hydroxymethoxy through formic acid and formate formation, followed by dissociation to CO2. CH2O formation from methoxy dehydrogenation is considered to be the rate-limiting step for the three reactions. In general, the thermodynamic and kinetic preference of the three reactions shows the order methanol oxidation > MSR > methanol decomposition. Methanol oxidation and MSR are faster than methanol decomposition by about 500 and 85 times at typical catalytic conditions (e.g., 523 K), respectively. The result may be useful for computational design and optimization of Cu-based catalysts.

http://dx.doi.org/10.1016/j.ijhydene.2013.11.048

 

GULP

 

ChemShell—a modular software package for QM/MM simulations ß A review of QM/MM

ChemShell is a modular computational chemistry package with a particular focus on hybrid quantum mechanical/molecular mechanical (QM/MM) simulations. A core set of chemical data handling modules and scripted interfaces to a large number of quantum chemistry and molecular modeling packages underpin a flexible QM/MM scheme. ChemShell has been used in the study of small molecules, molecular crystals, biological macromolecules such as enzymes, framework materials including zeolites, ionic solids, and surfaces. We outline the range of QM/MM coupling schemes and supporting functions for system setup, geometry optimization, and transition-state location (including those from the open-source DL-FIND optimization library). We discuss recently implemented features allowing a more efficient treatment of long range electrostatic interactions, X-ray based quantum refinement of crystal structures, free energy methods, and excited-state calculations. ChemShell has been ported to a range of parallel computers and we describe a number of options including parallel execution based on the message-passing capabilities of the interfaced packages and task-farming for applications in which a number of individual QM, MM, or QM/MM calculations can performed simultaneously. We exemplify each of the features by brief reference to published applications.

http://dx.doi.org/10.1002/wcms.1163

 

Understanding the influence of grain boundary thickness variation on the mechanical strength of a nickel-doped tungsten grain boundary

Grain boundaries (GBs) in nickel (Ni)-doped tungsten (W) are found to have thickness as a function of the level of saturation of W atoms with respect to Ni atoms in the GBs. While the unsaturated Ni-doped W GBs have average thickness of approximately 0.3 nm, the saturated Ni-doped W GBs have twice the average thickness (∼0.6 nm). The present work examines (1 1 0)–(2 1 0) W GB mechanical strength as a function of thickness using an ab initio calculation framework based on Car–Parrinello molecular dynamics (CPMD) simulations. The atomic fraction of Ni atoms is varied to understand the influence of Ni addition and its correlation with thickness variation on the GB mechanical strength. In the case of GBs with 0.3 nm thickness, the variation of peak tensile strength as a function of Ni atomic fraction variation from 5% to 50% is negligible. However, in the case of 0.6 nm GB, the changes in the peak tensile strength are significant with the maximum peak tensile strength observed in the case of 58% Ni atomic fraction. Analyses examine electron density of states and phonon dispersion relations to delineate the role of atomic level bond strength in thickness dependent GB mechanical strength. The thickness dependent GB strength variation is found to be strongly correlated to the thickness dependent change in lower acoustic mode phonon frequencies. At the same time Ni atomic fraction dependent change in GB strength is found to be strongly correlated to the corresponding changes in electron density of states. Based on the analyses performed, an analytical relation to predict GB peak tensile strength as a function of atomic cohesive energy, GB thickness (level of saturation), and the Ni atomic fraction is proposed.

http://dx.doi.org/10.1016/j.ijplas.2013.07.010

 

Effects of threshold displacement energy on defect production by displacement cascades in α, β, and γ-LiAlO2 

Threshold displacement energy evaluation and a series of displacement cascade simulations in α, β, and γ-LiAlO2 were performed using molecular dynamics. Threshold displacement energy evaluations indicated that higher absolute ionic charge values and larger densities both increase threshold displacement energy. The displacement cascade simulations suggest that the influence of different crystal structures on the number of interstitial atoms generated in a displacement cascade is explainable almost entirely by the difference of the threshold displacement energy.

http://dx.doi.org/10.1016/j.jnucmat.2013.05.048