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Equiatomic binary phases of copper with rare earth (RE) elements exhibit either primitive cubic (Pm3̄m) or orthorhombic (Pnma) structures and in some cases both. By using density functional theory (DFT), we calculated the enthalpies of formation along the series of RE elements combined equimolarly with copper. For RE from Sc to Lu, the calculated enthalpies of formation fall in the range -49.8 kJ/mol for LuCu to -9.1 kJ/mol for the least thermodynamically stable CeCu. Except NdCu, all the other cubic or orthorhombic compounds exhibit lattice stability. Either forms of NdCu indicated lattice instability. Along the Sc-group, the hypothetical primitive cubic and orthorhombic forms of LuCu are found thermodynamically and mechanically stable. The overall trend of the formation enthalpies as a function of the Meyer Periodic Number is consistent with the energy trend of the 4f-orbital filling as moving from Sc to Lu monocuprides. In addition, the calculated Gibbs free energies indicate that the thermodynamic stability is largely due to the entropic contributions. All standard DFT calculations were also repeated with DFT+U to better describe the correlation between the 5d-4f and 3d shells of RECu compounds. It has been found that DFT+U slightly affects the enthalpies of formation of RECu binaries. Moreover, DFT+U shifts up the f-band energies of RECu with light RE elements (such as La, Ce and Pr) and in contrast lowers them in the case of RECu with heavy RE elements from Nd to Lu.

The structural, electronic, optical, and thermo-electric properties of LuNiBi and LuNiSb Half-Heusler have been studied using a full potential linearized augmented plane-wave (FP-LAPW) method. The results of the calculations presented in this work were obtained through the use of different approximations GGA-PBE, GGA-PBEsol, GGA-WC, and mBJ-GGA. The electronic band structures exhibit that the LuNiBi and LuNiSb alloys have a small indirect gaps in the valence band and the conduction band at points Г and X, revealing the semiconductor character in both compounds. The complex dielectric function e (ω), optical conductivity σ (ω), extinction coefficient к (ω), refractive index n (ω), and reflectivity R (ω) as a function of photon energy are calculated using mBJ-GGA approximation, that is yielding results in good accordance with available experimental data. On the other hand, the variations of the thermal conductivity, power factor, figure of merit ZT, Seebeck coefficient, and electrical conductivity, as a function of temperature, have been investigated. Most of the optical and thermoelectric properties of LuNiSb and LuNiBi materials are not available in the literature; this makes the present work as a detailed comparative study between both compounds and opens the path for other future accurate theoretical studies to find the promising substitute for the interesting and more efficient thermoelectric device in industry.

Dual-cation ammine metal borohydrides are favorable hydrogen storage materials due to their high gravimetric density and relatively low hydrogen release temperature. By combining the Fast and Flexi...

A new algorithm called Fast and Flexible CrystAl Structure Predictor (FFCASP) was developed to predict the structure of covalent and molecular crystals. FFCASP is massively parallel and able to handle more than 200 atoms in the unit cell (in other terms, it allows global optimization around 100 individual parameters). It uses a global optimizer specialized for Crystal Structure Prediction (CSP) which combines particle swarm and simulated annealing optimizers. Three different molecular crystals, including diverse intermolecular interactions, namely, cytosine, coumarin, and pyrazinamide, have been selected to evaluate the performance of FFCASP. While cytosine polymorphs have been searched by employing two different force fields (a DFT-SAPT based intermolecular potential and generalized amber force field (GAFF)) up to Z = 16, only GAFF has been used both in coumarin and pyrazinamide polymorph searches up to Z = 4. For these three molecular crystals, FFCASP generated more than 20 000 crystal structures, and the unique ones have been further treated by DFT-D3. A combination of data mining and a machine learning approach was introduced to determine the unique structures and their distribution into different clusters, which ultimately gives an opportunity to retrieve the common features and relations between the resulting structures. There are two known experimental crystal structures of cytosine, and both were successfully located with FFCASP. Two of the reported crystal structures of coumarin have been reproduced. Similarly, in pyrazinamide, three known experimental structures have been rediscovered. In addition to finding the experimentally known structures, FFCASP also located other low-energy structures for each considered molecular crystals. These successes of FFCASP offer the possibility to discover the polymorphic nature of other important molecular crystals (e.g., drugs) as well.

We have designed and synthesized a pair of highly asymmetric D-aA-D′ type pyridyl-sulfonyl based isomers comprising phenothiazine (PTZ) and carbazole (Cz) donor units, which are able to emit thermally activated delayed fluorescence. PTZ-pS4-Py-2Cz and PTZ-mS4-Py-2Cz both possess spatial separation of HOMO/LUMO on the donor and acceptor moieties, resulting in small calculated singlet–triplet energy gaps (~0.25 eV). Both isomers exhibit dual emission, which is attributed to charge transfer states associated with the Cz and PTZ moieties at higher and lower energies, respectively. Photoluminescence quantum yields and time-resolved emission decays show significant differences for the two isomers, with the para- isomer exhibiting more efficient emission and stronger delayed fluorescence than the meta- isomer – in strong contrast to recently reported analogous Cz-Cz D-aA-D isomers. The findings clearly show that the interconversion of triplets via the rISC mechanism is promoted when parallel Cz and PTZ charge transfer states are allowed to interact, explaining the improved performance of the Cz-PTZ materials compared to the previous Cz-Cz ones. Finally, moderate device performance was achieved in warm-yellowish (CIE; 0.41; 0.53 & 0.49; 0.48) non-doped OLEDs, which exhibited 0.5% & 1.9% maximum external quantum efficiencies for the meta- and para- isomers, respectively.

The toxic profile of chemical cross-linkers used in enhancing the stability of self-assembled nanomicelles made of amphiphilic polymeric materials hinders their use in clinical applications. This study was aimed to use the layered structure of Na-montmorillonite (MMT) as a stabilizer for nanomicelles made of poly(D,L-lactide-co-glycolide) (PLGA) amphiphilic polymer. The size of Na-MMT was reduced below 40 nm (nano-MMT) by processing in an attritor prior to its incorporation with PLGA. Hybrid PLGA nano-MMT (PM) nanoparticles (NPs) were prepared using dialysis nanoprecipitation. The size distribution was measured using dynamic light scattering (DLS). Loading 1250 mu g of the model drug molecule curcumin to PM (PMC) resulted in obtaining 88 nm-sized particles, suitable for passive targeting of cancer tumors. The structure of nano-MMT and its position in PMC were investigated using FT-IR, differential scanning chalorimetry (DSC), XRF, XRD, ESEM, and EDAX assays, all of which showed the exfoliated structure of nano-MMT incorporated with both hydrophilic and hydrophobic blocks of PLGA. Curcumin was mutually loaded to PLGA and nano-MMT. This firm incorporation caused a serious extension in the release of curcumin from PMC compared to PLGA (PC). Fitting the release profile to different mathematical models showed the remarkable role of nano-MMT in surface modification of PLGA NPs. The ex vivo dynamic model showed the enhanced stability of PMC in simulated blood flow, while cytotoxicity assays showed that nano-MMT does not aggravate the good toxic profile of PLGA but improves the anticancer effect of payload. Nano-MMT could be used as an effective nontoxic stabilizer agent for self-assembled NPs.

There is a lack of consensus on the crystal structure and polymorphism of Cu(I)-TCNQ, even though an enormous work and great achievements have been reported along decades. This motivated us to perform a crystal structure prediction study (by using FFCASP) combined with total energy calculations at DFT-D level. The ensemble of the optimized structures falls in two distinct regions based on the energy-density phase space. Our predictions located the thermodynamic phase (as a global minimum) and a conformationally similar local minimum structure to the experimentally proposed phase I, in the low- and high-density regions respectively. The Rietveld refinement of P2 1 2 1 2 local minimum structure to the experimental XRD pattern resulted in a structure with a density between the two regions. This polymorph, the kinetic product, becomes a high energy local minimum structure after the full geometry optimization, being 35.03 kJ/mol above the global minimum. In addition, we found that the transition from the high-...

Lithium and molybdenum do not form binary phases under thermodynamic control, but they might do under kinetic control upon lithiation of MoS 2 . High Lithiation of MoS 2 can either lead to high-lithiated phases [1] or form Li-Mo phases at the lithiation point at which decomposition in Li 2 S and elemental molybdenum can occur. First-principles crystal structure prediction calculations suggest that the LiMo, monoclinic structure, and Li 2 Mo , either orthorhombic or tetragonal structures, can be formed under kinetic control as co-products of the overall process of lithiation of MoS 2 . The computed enthalpies of formation of the Li-Mo phases vary considerably if the long-range dispersion interactions are accounted in for the elemental lithium and molybdenum.

Molecular clusters of 1,3-butadiene were theoretically investigated using a variety of approaches, encompassing classical force fields and different quantum chemical (QC) methods, as well as density-functional-based tight-binding (DFTB) in its self-consistent-charge (SCC) version. Upon suitable reparametrization, SCC-DFTB reproduces the energy difference and torsional barrier of the trans and gauche conformers of the 1,3-butadiene monomer predicted at the QC level. Clusters of pure trans and gauche conformers containing up to 20 monomers were studied separately, their energy landscapes being explored using the force fields, then locally reoptimized using DFT or SCC-DFTB. The all-trans clusters are generally found to be lower in energy and produce well-ordered structures in which the planar molecules are arranged according to a herringbone motif. Clusters of molecules in the gauche configuration are comparatively much more isotropic. Mixed clusters containing a single gauche molecule were also studied and found to keep the herringbone motif, the gauche impurity usually residing outside. In those clusters, the strain exerted by the cluster on the gauche molecule leads to significant geometrical distortion of the dihedral angle already at zero temperature. Finally, the finite temperature properties were addressed at the force field level, and the results indicate that the more ordered all-trans clusters are also prone to sharper melting mechanisms., ANR JCJC FRAPA; French Agence Nationale de la Recherche; GDR EMIE

Phytochemicals such as curcumin have great potential in cancer prevention and treatment. However, instability and low aqueous solubility of free curcumin weaken its anticancer potential. These undesirable problems can be avoided upon loading curcumin into nanoparticles containing biocompatible and biodegradable polymers such as poly lactic-co-glycolic acid (PLGA), liposomes or micelles. The interaction of drugs and release control can be further enhanced upon inclusion of clay minerals into the PLGA containing nanoparticles. Such nanoparticles offer a new way for cancer drug delivery systems. However, the role of the clay mineral in the resulting composite is not fully understood. Therefore, in this study, we carried out systematic adsorption studies of curcumin anticancer drug on montmorillonite (MMT) nanoparticles in the presence of amphiphilic polymer (PLGA) and in an aqueous environment to understand the contribution of the layered clay structure using cluster (B97-D), periodic DFT and molecular dynamics (MD) simulations in acidic and natural pH media. It has been found that MMT has high affinity towards either polymer or drug molecules especially due to vdW interactions. Furthermore, it has been observed that MMT facilitates the release of curcumin. Current findings suggest that a composite consisting of MMT and PLGA might be used to deliver the anticancer agent curcumin. Türkiye Bilimsel Ve Teknolojik Araştırma Kurumu ( Tübitak )

The interaction between hydrogen and carbonaceous nanostructures is of fundamental interest in various areas of physical chemistry. In this contribution we have revisited the physisorption of hydrogen molecules and H2 clusters on fullerenes, following a first-principles approach in which the interaction is quantitatively evaluated for the C20 system using high-level electronic structure methods. Relative to coupled cluster data at the level of single, double, and perturbative triple excitations taken as a benchmark, the results for rotationally averaged physisorbed H2 show a good performance of MP2 variants and symmetry-adapted perturbation theory, but significant deviations and basis set convergence issues are found for dispersion-corrected density functional theory. These electronic structure data are fitted to produce effective coarse-grained potentials for use in larger systems such as C60–H2. Using path-integral molecular dynamics, the potentials are also applied to parahydrogen clusters solvated aro...

A new intermolecular interaction potential for the adenine dimer has been developed with the help of a combination of symmetry-adapted perturbation theory and density functional theory (DFT-SAPT). Supermolecular intermolecular interaction energy computations on hydrogen-bonded and stacked adenine dimers at B3LYP-D, MP2, SCS-MP2, SCS-MI-MP2 and CCSD(T) levels showed that DFT-SAPT is in a very good agreement with CCSD(T). The developed ab initio intermolecular potential has been used to predict the cluster structure of adenine dimers, trimers and tetramers. These global cluster optimizations reproduced adenine dimers reported in the literature and moreover new low-energy structures were also located. For trimers and tetramers, new hydrogen-bonded and stacked low-energy structures have also been found. The current findings suggest that the new ab initio potential can further be exploited to reveal the structure and energy of much larger supramolecular adenine clusters.

Sepiolite is a fibrous clay mineral and consists of 2:1 silicate blocks connected at the corners and separated by tunnels (channels on external surfaces) that extend in the direction of fiber length. The tunnels, 3.7 A × 610.6 A in cross-section, are responsible for the incorporation of organic and inorganic compounds. The present study aimed to examine the capacity of twelve different organic molecules, such as pyridine, indigo, methylene blue, and quaternary amines, to gain access to the tunnels of sepiolite using quantum chemistry techniques. The interaction energy computations performed at the B97-D/TZVP level showed that all of the considered organic molecules tend to access the tunnels of sepiolite if external water molecules are absent. This finding is in agreement with experimental studies that included pyridine, indigo, 2,2-bipyridyl, and methylene blue. Interestingly, 2,6-dimethyl pyridine preferred to remain in a tunnel rather than an external channel of the sepiolite.

A new ab initio potential for the thymine dimer has been developed by using a combination of density functional theory and symmetry-adapted perturbation theory (DFT-SAPT). It has been shown that DFT-SAPT is in very good agreement with the reference CCSD(T) calculations performed for the hydrogen-bonded and stacked thymine dimers. Parallel global cluster optimizations have been carried out employing the new force field from the dimer to n = 50. It has been observed that the resulting cluster structures tend to form the building blocks of the crystal structure of thymine. This study therefore highlights the importance of dimer potentials to gain insights about the crystal structures. Published under license by AIP Publishing.

Phthalocyanines (Pcs) generally have a strong tendency for stacking in solution to form dimer and high order oligomers owing to the p-p, metal-ligand coordination, hydrogen bonding and donor-acceptor interactions between planar rings. Large substituents in peripheral positions, solvents and their amount and the central metal affect the aggregation to a remarkable extent. In Pcs, aggregation results in lowering the solubility, bringing purification and characterization problems and decreasing the photosensitizing efficiency. The aim of this study is to determine the predominant reasons inhibiting the aggregation in an unsymmetrically substituted metal-free Pc which contains three naphthoxy units and one carboxy1,2- dioxyphenyl in THF. Dispersion-corrected density functional theory interaction energy calculations performed at B97-D/TZVP level revealed that aggregation in these complexes are prevented due to the strong solvent-phthalocyanine interactions rather than the existence of large substituents. (C) 2015 Elsevier B.V. All rights reserved.

We developed a new first principles potential for the cytosine dimer. The ab initio calculations were performed with a DFT-SAPT combination of the symmetry-adapted perturbation method and density functional theory, and fitted to a model site-site functional form. The model potential was used to predict cluster structures up to cytosine hexamers. The global cluster structure optimizations showed that the new potential is able to reproduce some of the 2D filament structures. Moreover many new non-planar cytosine cluster structures were also discovered. Interaction energies of these clusters were compared with B3LYP-D, MP2, SCS-MP2, SCS-MI-MP2 and AMBER. It has been shown that the model agrees well with all ab initio methods, especially for the cytosine hexamer. The model potential outperforms the AMBER force field and therefore it can be exploited to study more challenging larger systems.

Zinc (II) phthalocyanines, bearing peripherally β-naphthol and ({1-[(Z or E)-phenylazo]-2-naphthyl}oxy) have been synthesized and characterized. Aggregation properties of these compounds were investigated in different concentration ranges. The molecular orbital properties and ultraviolet–visible spectra of these phthalocyanines were studied using density functional and time-dependent density functional theories. The computed electronic spectra are in good agreement with the experimental data. Moreover, dimerization of these phthalocyanine complexes in solvent (tetrahydrofuran) medium was investigated by counterpoise corrected interaction energy calculations employing dispersion corrected Becke's 1997 hybrid functional with valence triple-zeta basis set. These calculations revealed that aggregation in these complexes are prevented due to the strong solvent–phthalocyanine interactions and this finding was supported by our experiments.

Herein, some fundamental open questions on engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials are considered, namely: 1) on thermodynamic stability and related characteristics of some hydrogenated graphene layers nanostructures: relevance to the hydrogen storage problem; 2) determination of thermodynamic characteristics of graphene hydrides; 3) a treatment and interpretation of some recent STM, STS, HREELS/LEED, PES, ARPS and Raman spectroscopy data on hydrogensorbtion with epitaxial graphenes; 4) on the physics of intercalation of hydrogen into surface graphene-like nanoblisters in pyrolytic graphite and epitaxial graphenes; 5) on the physics of the elastic and plastic deformation of graphene walls in hydrogenated graphite nanofibers; 6) on the physics of engineering of “super” hydrogen sorption (storage) in carbonaceous nanomaterials, in the light of analysis of the Rodriguez-Baker extraordinary data and some others. These fundamental open questions may be solved within several years.

Isomer- and mass-selective UV and IR-UV double resonance spectra of the BA3, B2A, and B2A2 clusters of benzene (B) and acetylene (A) are presented. Cluster structures are assigned by comparison with the UV and IR spectra of benzene, the benzene dimer, as well as the BA, BA2, and B2A clusters. The intermolecular vibrations of BA are identified by dispersed fluorescence spectroscopy. Assignment of the cluster structures is supported by quantum chemical calculations of IR spectra with spin-component scaled second-order Møller-Plesset (SCS-MP2) theory. Initial propositions for various structures of the BA3 and B2A2 aggregates are generated with model potentials based on density functional theory combined with the symmetry-adapted perturbation theory (DFT-SAPT) approach. Shape and relative cluster stabilities are then confirmed with SCS-MP2. T-shaped geometries are the dominant structural motifs. Higher-energy isomers are also observed. The detected cluster structures are correlated with possible cluster formation pathways and their role as crystallization seeds is discussed.

We report a first-principles structure prediction of the LiBH(2), which structures are modeled by using four formula units per unit cell without symmetry restrictions. The computational methodology combines a simulated annealing approach and density functional total energy calculations for crystalline solid structures. The predicted lowest energy structure shows the formation of linear anionic chains, (∞)(1)[BH(2)], enthalpy of formation at 0 K equal to -90.07 kJ/mol. Ring structures, in particular with butterfly and planar square topologies, are found to be stable but well above the ground state by 20.26 and 12.92 kJ/mol, respectively. All convergent structures fall in the symmetry families monoclinic, tetragonal, and orthorhombic. For the representative structures of each family group, simulated X-ray diffraction patterns and infrared spectra are reported.

Crystal structure prediction from first principles is still one of the most challenging and interesting issue in condensed matter science. we explored the potential energy surface of NaBH4 by a combined ab-initio approach, based on global structure optimizations and quantum chemistry. In particular, we used simulated annealing (SA) and density functional theory (DFT) calculations. The methodology enabled the identification of several local minima, of which the global minimum corresponded to the tetragonal ground-state structure (P42/nmc), and the prediction of higher energy stable structures, among them a monoclinic (Pm) one was identified to be 22.75 kJ/mol above the ground-state at T=298 K. In between, orthorhombic and cubic structures were recovered, in particular those with Pnma and F 4 ¯ 3 m symmetries.

A computational screening study consisting of crystal structure prediction and density functional theory has been performed for dual-cation ammine metal borohydrides (AMBs) with a general formula of M1M2(BH4)(3)(NH3)(2-6) (M-1 = Li, Na, or K and M-2 = Sr, Ca, Mg, Zn, Mn, or Ni). The stability and decomposition energies of the resulting 90 alloys were used for the evaluation of the screening. It has been observed that two recently synthesized dual-cation AMBs (LiMg(BH4)(3)(NH3)(2) and NaZn(BH4)(3)(NH3)(2)) are predicted to form stable alloys. Moreover, the M-1 (Mn,Mg) (BH4)(3)(NH3)(2-6) and M1Ni(BH4)(3)-(NH3)(4-6) alloys, which are not synthesized yet, are also found to be promising.

Si n clusters in the size range n = 4–30 have been investigated using a combination of global structure optimization methods with DFT and ab initio calculations. One of the central aims is to provide explanations for the structural transition from prolate to spherical outer shapes at about n = 25, as observed in ion mobility measurements. Firstly, several existing empirical potentials for silicon and a newly generated variant of one of them were better adapted to small silicon clusters, by global optimization of their parameters. The best resulting empirical potentials were then employed in global cluster structure optimizations. The most promising structures from this stage were relaxed further at the DFT level with the hybrid B3LYP functional. For the resulting structures, single point energies have been calculated at the LMP2 level with a reasonable medium-sized basis set, cc-pVTZ. These DFT and LMP2 calculations were also carried out for the best structures proposed in the literature, including the most recent ones, to obtain the currently best and most complete overall picture of the structural preferences of silicon clusters. In agreement with recent findings, results obtained at the DFT level do support the shape transition from prolate to spherical structures, beginning with Si 26 (albeit not completely without problems). In stark contrast, at the LMP2 level, the dominance of spherical structures after the transition region could not be confirmed. Instead, just as below the transition region, prolate isomers are obtained as the lowest-energy structures for n ≤ 29. We conclude that higher (probably multireference) levels of theoretical treatments are needed before the puzzle of the silicon cluster shape transition at n = 25 can safely be considered as explained.

Global energy need is mostly fulfilled via fossil fuels. Usage of these sources causes harmful consequences to both environment and human beings. Besides, they have limited reserves and therefore alternative fuels must be discovered. Hydrogen is one of these alternatives due to its high energy content and environmentally friendly nature. However, there are many challenging problems waiting to be addressed for its widespread use. One of them is hydrogen storage which is especially very important for on-board applications. Even hydrogen can be stored as in the form of gas or liquid, these mediums are not practical in everyday use. As an alternative, hydrogen can also be stored in the solid form. For this purpose, both metal borohydrides and ammines are proposed due to their high gravimetric and volumetric densities. Metal borohydrides have some severe drawbacks e.g., requirement of a very high temperature for the hydrogen decomposition. Therefore, they can be mixed with ammines to produce new materials with a better thermodynamics. Dual-cation ammine metal borohydrides (AMBs) just suit well for this purpose. In this study, we computationally designed new AMBs in the form of LiTi(BH4)5(NH3)x x = 2, 3, 4 using a strategy which combines crystal structure prediction with density functional theory computations.

World’s growing energy need is mostly reliant upon fossil fuels. Fossil fuels are considered to be non-renewable energy sources because it needs million years to form and reserves are being depleted much more faster than new reserves are being made. Usage of fossil fuels comes with harmful consequences. It is responsible for 20 % of global warming pollution. To avoid these harmful effects, new energy sources must be discovered. As an alternative to fossil fuels, hydrogen can be used for energy needs and it has a lot of benefits over fossil fuels such as being environmentally friendly, carrying high energy content and being renewable. To use hydrogen as an energy source instead of fossil fuels, some challenging problems must be solved. One of them is hydrogen storage. Hydrogen can be stored as gas or liquid but these types of storage are not so efficient for widespread use. A more convenient way is to store hydrogen in the form of solid. For this purpose, metal borohydrides and ammines can be used due to their high gravimetric and volumetric densities. To decompose hydrogen, metal borohydrides requires very high temperatures and this situation can be moderated by mixing them with ammines. To achieve this goal, in this study we designed dual-cation ammine metal borohydrides (AMBs) in the form of LiSc(BH4)4(NH3)x (x = 2, 3) using an approach which combines crystal structure prediction with density functional theory computations.

Hydrogen is one of the promising alternatives for the replacement of fossil-fuels. One of the major bottlenecks preventing its widespread commercialization for on-board applications is to find the most suitable storage medium. Metal borohydrides are one of the classes of solid materials studied intensively to store hydrogen due to their high theoretical hydrogen capacities. However, their high thermodynamic stability is one of the major problems limiting their usage. The requirement of high decomposition temperature can be lowered by the inclusion of ammonia. The resulting new complex containing both borohydrides and ammines is called as Ammine Metal Borohydrides (AMBs). However, some of the AMBs have insuppressible release of ammonia during the dehydrogenation. This can be solved by the inclusion of a second metal atom into AMBs leading to dual-cation AMBs with a general formula of M1M2(BH4)y(NH3)x. Experimental studies about one dual-cation AMBs (LiMg(BH4)3(NH3)2) indicate desired properties e.g., decomposition occurs below 200 °C and no release of ammonia. In this study, a computational screening using periodic density functional theory was performed to find promising dual-cation AMBs (M1M2(BH4)y(NH3)x with M1 = Li, Na, K, M2 = Mg, Ca, Sr, Zn, Mn, Ni, y = 3, x = 2, 3, 4, 5, 6). The screening has been accomplished using template crystal structures generated by Crystal Structure Prediction via Simulated Annealing (CASPESA) method. Formation, alloying and simple decomposition reactions were employed for the evaluation of the complexes.

The applied thermodynamic aspects of removing hydrogen, nitrogen, oxygen, carbon, and silicon from vanadium, niobium and tantalum metals by pyrovacuum treatments are considered in this paper. Two major processes operate in refining by pyrovacuum treatment. One is distillation and the other is degassing. Distillation is mainly used to remove substitutional impurities that are either already present in the metal or have been added for removing any interstitial impurity. The success is determined by the partial pressure of the impurity element as well as by the difference in partial pressures of the impurity and the metal. The maximum rate of vaporization of impurity can then be estimated using the free evaporation equation. Interstitial impurities, particularly the gases hydrogen, nitrogen and oxygen, are removed by degassing. Thermodynamics of classical degassing, which is essentially the reverse of absorption, is described usefully by the pressure-composition isotherms. This is applicable mainly for the r...

The ab initio intermolecular potential of guanine has been developed with the help of a combination of symmetry-adapted perturbation theory and density functional theory (DFT). The resulting potential has been globally optimized to locate the guanine cluster structures up to tetramers. It has been found that the new potential is able to reproduce the known guanine cluster structures, especially the guanine quartet stabilized by Hoogsteen hydrogen bonds, in addition to new low-energy conformers. The performance of the potential was also compared with the AMBER force field as well as DFT-D and MP2 levels of theory. The model potential is in agreement with the ab initio methods and it shows a better performance compared to AMBER. Therefore, it can be further exploited in molecular dynamics or global optimizations to determine the structure and energy of much larger guanine clusters. Published by AIP Publishing.

Metal matrix composites, prepared by pressure infiltration casting of copper base alloy into 2 types of microporous carbon preforms, one with 100% amorphous carbon and the other containing 40 wt pct. graphite and 60 wt pct. amorphous carbon, have been examined for their wear and friction behavior under ambient conditions using a pin-on-plate reciprocating wear tester. Micro-structural characterization of tribo-surfaces has been carried out. The thin carbon films formed on the tribo-surface reduced the friction coefficient and wear for the composites, especially at low loads on the pin. Adhesive wear observed on the tribo-surface promoted wear and friction at high loads. The wear and friction were observed to be very sensitive to the size and distribution of the microstructural constituents.

Refractory metals belonging to the Group IV-VIB of the periodic table are conventionally produced from their natural sources by a sequence of pyro and hydro-metallurgical process first to produce a pure chemical intermediate which is then reduced to crude metal. The physical, chemical and mechanical properties of the metal are very sensitive to the presence of metallic and interstitial impurities. The reduced crude metal is usually subjected to post reduction purification treatment to obtain pure metals. For certain specific applications it is further necessary to purify the metals to still higher purity. This paper briefly reviews the present status on purification of refractory metals such as titanium, zirconium, hafnium, niobium, tantalum, vanadium, molybdenum and tungsten and also presents directions for future research in the field of these metals.

On-board hydrogen storage for transportation applications continues to be one of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled vehicles. In addition, hydrogen storage is also required for off-board purposes such as stationary power generation and hydrogen delivery and refueling infrastructure. After decades of extensive exploration, research into hydrogen storage materials based on metal borohydrides has become a highly active and exciting area owing to the high theoretical hydrogen capacities of these materials. However, they are thermodynamically too stable and therefore a very high temperature is required for their decomposition. This temperature can be lowered to the tolerable levels by the addition of ammonia and the resulting material is called as Ammine Metal Borohydrides (AMBs). In this study, we aim to search the ground state crystal structures of LiMg(BH4)3(NH3)x [1] with x = 2, 3, 4 using CrystAl Structure Prediction via Simulated Annealing (CASPESA) method. This approach was successfully located the experimentally determined structure of LiMg(BH4)3(NH3)2 [1] and other interesting local minima. For x = 3 and 4 cases, our methodology also resulted new crystal phases.

The technique of explosive consolidation was used to prepare cermets of boron carbide with aluminium and 7075 aluminium alloy. Compacts were produced by application of 10–12 GPa pressure which was induced by explosive detonation. The compacts obtained exhibit high hardness-increasing with an increase in the boron-carbide content, integrity and close to theorical density. Hardness, fracture toughness and flexural strengths of the composites produced indicate extensive shock hardening of the metal (or alloy) matrix during consolidation.

The possibility of producing aluminium matrixed aluminium nitrideboron carbide composites by pressureless wetting assisted infiltration has been shown. Cold isostatically pressed cup-shaped preforms of boron carbide (1–10 wt%) aluminium nitride mixtures were sintered at 1400–1600 °C in nitrogen atmosphere and then infiltrated with aluminium under 6.5 kPa argon at 1250 °C. Pore diameter in the preforms increased with increase in sintering temperature. Infiltrated samples which were sectioned and polished showed no infiltration front. Higher B 4 C contents (4–10%) and sintering temperature (1600 °C) resulted in full infiltration. In the sintered preforms AlN was the only phase observed. However, in the infiltrated materials both AlN and Al were observed.

Two methods for the preparation of magnetic iron oxide starting from FeSO4 · 7H2O are described. The traditional method involves preparation of Fe(OH)2 seed material, conversion of the seed to acicular γ-FeOOH crystals, dehydration of the crystals to α-Fe2O3, hydrogen reduction of Fe2O3 to magnetite, and finally reoxidation of magnetite particles to γ-Fe2O3. Magnetic iron oxide particles thus obtained, after a total processing time of about 25 h, have a coercivity between 330 and 380 Oe. The other method, known as the direct method, involves fewer steps, a shorter overall processing time, and yields magnetic iron oxide having an equivalent or higher coercivity value. A sample from the seed preparation solution is recrystallized at 250 °C, yielding a product, γ-Fe2O3, which has a coercivity value of 320 Oe. In another procedure the seed is prepared in the presence of H2O2 as the oxidizing agent and recrystallized at 300 °C for 2 h to yield γ-Fe2O3 having 390 Oe coercivity.

The formation and separation of metal nitrides from a variety of materials including ferroalloys, oxides, natural materials and minerals is an important component in current materials processing practice. Ferroalloys like ferroniobium and ferrovanadium undergo nitridation by ammonia yielding a mixture of iron nitrides and the refractory metal nitride. Acid leaching effectively separates the iron nitride from the mixture. Niobium nitride thus obtained is used to produce niobium metal by pyrovacuum treatment. Vanadium nitride converts to metal when pyrovacuum treatment is followed by electrorefining. Nitride suitable for decomposition to metal can be obtained from niobium pentoxide by reacting ammonia or by reacting a mixture of carbon and nitrogen. Rice husk is a ready-made intimate mixture of silica and carbon. It can be converted to silicon nitride or to a mixture of silicon carbide and silicon nitride by carbonitrothermic reduction. β sialon can be directly prepared from kaolinite by carbonitrothermic reduction. Ilmenite is another mineral amenable to nitridation processing. It yields after reaction with nitrogen in presence of carbon, a separable titanium nitride-iron mixture. All these attractive features of nitridation have been discussed in this paper. The possibility of incorporating nitridation into the process flowsheets has been highlighted.

Rice husk is a potentially useful source material for the production of silicon nitride, silicon carbide or a mixture of both. Pyrolysis of rice husk yields an intimate and homogeneous mixture of carbon and silica which is highly desirable for a good carbonitrothermic or carbothermic reduction process. The formation of Si 3 N 4 occurs on heating the pyrolysed rice husk to 1400°C under nitrogen flow and SiC forms in the presence of excess carbon at temperatures above 1450°C. SEM and XRD results show that the morphology of the nitride product is influenced by the reaction temperature and the presence of additives.

The processes for the production of ferroboron and ferrovanadium from indigenous resources by open aluminothermic reduction have been described. The influence of process parameters such as charge composition, particle size, and the use of fluxes on the yield and composition of the ferroalloys obtained are discussed. In the case of ferroboron, it has been possible to obtain a recovery of 60% of boron as Fe-15B while restricting the residual aluminium content in the product to approximately 2% by using 90% of stoichiometric aluminium in the charge. In the case of ferrovanadium, it has been possible to achieve a recovery of 70% of vanadium as Fe-75V by using 5% excess aluminium in the charge, with the same percentage remaining as residual aluminium in the product.

Carbothermic reduction of boric acid has scientific and economic advantages over other methods of boron carbide production. The strongly endothermic reaction which has a favourable free energy change only at high temperatures is best carried out in a specially designed graphite resistance furnace at temperatures above 2000 degrees C, using boric acid and petroleum coke as starting materials. The composition of the charge has a strong influence on the quality of boron carbide obtained and also on the yield. The use of boron anhydride in place of boric acid decreases the yield. The yield is also affected by the heating conditions prevailing in the furnace. The yield of boron carbide can be substantially improved and thus the specific energy consumption in boron carbide production can be significantly decreased by adding an optimum quantity of salt to the boric acid-petroleum coke mixture. The various factors that influence the quality and yield of boron carbide product and hence the economy of boron carbide production by the carbothermic reduction route have been discussed in this paper.

In materials science there is an increasing need for developing a robust and reliable first-principle approach capable of predicting crystal structures, by taking only the stoichiometry as an input. We integrate several methodologies to tackle this problem including quantum chemistry cluster calculations, simulated annealing algorithm for structure modelling, density functional theory total energy calculations and symmetry group analysis. A case study is Mg(BH(4))(2) in the aim to find the reasons for discrepancies between theoretically and experimentally proposed structures. In addition to new stable monoclinic, orthorhombic and tetragonal structures, a cubic one is suggested as a possible high energy structure. Moreover, the symmetry group analysis makes possible to link symmetry-related structures via group-subgroup relations, and subsequently identify local minima on the Potential Energy Surface.

π–π and CH···N interactions are vital in biological systems. In this study, stacking and hydrogen-bonded interactions in pyrazine and triazine dimers were investigated by density functional theory combined with symmetry-adapted perturbation theory (DFT-SAPT) and counterpoise (CP)-corrected supermolecular MP2, SCS-MP2, B3LYP-D and CCSD(T) calculations. All interaction energies were computed using the optimized structures at the CP-corrected SCS/aug-cc-pVDZ level, which gave 1–2 kJ/mol lower interaction energies than the ones computed at the MP2 level. For both dimers, doubly hydrogen-bonded and cross-(displaced) stacked orientations were found to be the lowest energy ones. The reference CCSD(T) calculations favored the former structure in both dimer systems, whereas MP2 and SCS-MP2 located the latter as the lowest energy isomer. In particular, the former was found to be lower in energy than the latter by 2.28 and 1.01 kJ/mol at the CCSD(T)/aug-cc-pVDZ level for pyrazine and triazine, respectively. B3LYP-D produced interaction energies in agreement with the CCSD(T) at the equilibrium geometries, but it overestimates them at the short range and underestimates at the long intermonomer separations. Furthermore, it tends to give smaller equilibrium distances compared to the CCSD(T). DFT-SAPT method was in a good agreement with the reference CCSD(T) calculations. This suggests that DFT-SAPT can be employed to compute the full potential energy surface of these dimers. Moreover, DFT-SAPT calculations showed that the electrostatic and dispersion contributions are the most important energy components stabilizing these dimers. The present study aims to show which theoretical method is the most promising one for the investigation of intermolecular interactions dominated by π–π and CH···N. Therefore, the findings obtained in this study can be used to unravel the structures of nucleic acid bases and other systems stabilized by π–π and CH···N interactions.

The microstructure of a semi-continuously cast AA 6063 alloy was investigated and the transformation of insoluble intermetallic phases by applied heat treatment was studied by selective dissolution of the matrix. Residual intermetallics were characterized using energy-dispersive X-ray analysis, X-ray and electron diffraction techniques. Transformation of β-AlFeSi phase, which is known to have detrimental effects on the surface finish of the extrudates, to more favourable α-AlFeSi phase by heat treatment was determined.

The infrared spectroscopy of molecules, complexes, and molecular aggregates dissolved in superfluid helium clusters, commonly called HElium NanoDroplet Isolation (HENDI) spectroscopy, is an established, powerful experimental technique for extracting high resolution ro-vibrational spectra at ultra-low temperatures. Realistic quantum simulations of such systems, in particular in cases where the solute is undergoing a chemical reaction, require accurate solute-helium potentials which are also simple enough to be efficiently evaluated over the vast number of steps required in typical Monte Carlo or molecular dynamics sampling. This precludes using global potential energy surfaces as often parameterized for small complexes in the realm of high-resolution spectroscopic investigations that, in view of the computational effort imposed, are focused on the intermolecular interaction of rigid molecules with helium. Simple Lennard-Jones-like pair potentials, on the other hand, fall short in providing the required flexibility and accuracy in order to account for chemical reactions of the solute molecule. Here, a general scheme of constructing sufficiently accurate site-site potentials for use in typical quantum simulations is presented. This scheme employs atom-based grids, accounts for local and global minima, and is applied to the special case of a HCl(H(2)O)(4) cluster solvated by helium. As a first step, accurate interaction energies of a helium atom with a set of representative configurations sampled from a trajectory following the dissociation of the HCl(H(2)O)(4) cluster were computed using an efficient combination of density functional theory and symmetry-adapted perturbation theory, i.e. the DFT-SAPT approach. For each of the sampled cluster configurations, a helium atom was placed at several hundred positions distributed in space, leading to an overall number of about 400,000 such quantum chemical calculations. The resulting total interaction energies, decomposed into several energetic contributions, served to fit a site-site potential, where the sites are located at the atomic positions and, additionally, pseudo-sites are distributed along the lines joining pairs of atom sites within the molecular cluster. This approach ensures that this solute-helium potential is able to describe both undissociated molecular and dissociated (zwitter-) ionic configurations, as well as the interconnecting reaction pathway without re-adjusting partial charges or other parameters depending on the particular configuration. Test calculations of the larger HCl(H(2)O)(5) cluster interacting with helium demonstrate the transferability of the derived site-site potential. This specific potential can be readily used in quantum simulations of such HCl/water clusters in bulk helium or helium nanodroplets, whereas the underlying construction procedure can be generalized to other molecular solutes in other atomic solvents such as those encountered in rare gas matrix isolation spectroscopy.

The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides. © 2011 the Owner Societies.

We report the definition and refinement of a new first principles potential for the acetylene dimer. The ab initio calculations were performed with the DFT-SAPT combination of symmetry-adapted intermolecular perturbation method and density functional theory, and fitted to a model site-site functional form. Comparison of the calculated microwave spectrum with experimental data revealed that the barriers to isomerization were too low. This potential was refined by fitting the model parameters in order to reproduce the observed transitions, an excellent agreement within ~1 MHz being achieved.

The potential energy surface of LiBH4 is investigated by a ground-state search method based on simulated annealing and first-principles density functional theory calculations. A new stable orthogonal structure with Pnma symmetry is found, which is 9.66 kJ/mol lower in energy than the proposed Pnma structure by Soulié et al. [J. Alloys Compd. 346, 200 (2002)]. For the high-temperature structure, we suggest a new monoclinic P2/c structure, which is 21.26 kJ/mol over the ground-state energy and shows no lattice instability.