Ab initio calculation of stable structures of a Na atomic chain under bias voltages

The stable geometries of a three-atom Na chain connected to two semi-infinite jellium electrodes are studied under bias voltages by performing ab initio force calculations within the density functional theory. At a low bias voltage of 0.01 V, the stable geometry is found to be symmetric, while it becomes asymmetric for higher bias voltages. The displacements of Na atoms in the chain are proportional to the applied bias voltages up to 1 V, while their behavior changes drastically above 1 V. These results can be understood from the behavior of charges induced by the applied voltage. It is also found that the structural relaxation due to the bias voltage also affects the potential drop along the chain and the current–voltage characteristics of the chain.     

Ab initio study on geometrical structures of the TTTA molecular crystal

The crystal made of organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), exhibits a large first-order magnetic and structural phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-temperature (LT) phase, with a surprisingly wide thermal hysteresis loop over room temperature. We investigate theoretically the crystal structures for the two phases by means of the ab initio structural optimization method based on the local density approximation. We present necessary and sufficient atomic coordinates in this paper. The resulting structures are in good agreement with the recent X-ray diffraction experiment. In the HT phase, uniform one-dimensional stacking of the radical molecule appears, while, in the LT phase, strong dimerization along the stacking direction appears.     

Ab initio study on geometrical structures of the TTTA molecular crystal

The crystal made of organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA), exhibits a large first-order magnetic and structural phase transition between a paramagnetic high-temperature (HT) phase and a diamagnetic low-temperature (LT) phase, with a surprisingly wide thermal hysteresis loop over room temperature. We investigate theoretically the crystal structures for the two phases by means of the ab initio structural optimization method based on the local density approximation. We present necessary and sufficient atomic coordinates in this paper. The resulting structures are in good agreement with the recent X-ray diffraction experiment. In the HT phase, uniform one-dimensional stacking of the radical molecule appears, while, in the LT phase, strong dimerization along the stacking direction appears.     

Ab initio study of magnetic coupling in aniline-based molecules: Role of Fe atoms

Our interest is the study of magnetic properties of organic compounds. We have previously reported a new class of organic magnets based on aniline and aminonaphthalenesulfonic acid. In this work, we explore theoretically a simple model based on superposed aniline molecules (radicals) and Fe atoms to determine the mechanism that stabilizes the parallel alignment of the electronic spin. Calculations were performed within the non-local spin density approximation with Becke's exchange functional and the gradient-corrected functional of Lee, Yang and Parr (BYLP) using the DMol program. The results show a high sensitivity of the magnetic properties to the oxidation state of the metal: intercalated between molecular aniline the total spins are 1, 0 and 1/2 for Fe0, FeII and FeIII, and between radicals the spins are 0, 0 and 1/2, respectively. This opens the possibility of creating molecular magnets by doping purely organic materials with transition metal atoms or ions.     

Ab initio calculations of Fe–Ni clusters

The clusters of Fe, Ni, and Fe–Ni are investigated computationally using a density functional approach. The geometries of clusters are optimized under the constraint of well-defined point group symmetries at the UB3LYP/LanL2DZ level. The equilibrium geometries and binding energies are presented and discussed, together with natural populations and natural electron configurations. In addition, the binding energies of Fe_n−xNi_x clusters are found to generally decrease by successive substitutions of Ni atoms for Fe atoms. For Fe_n−xNi_x clusters, the comparisons on total energies between isomers indicate that Ni atoms energetically prefer clustering in the mixed Fe–Ni clusters. The calculations for Fe_n−xNi_x clusters show that the clustering leads to a segregation of Ni atoms from Fe atoms.     

Initial reaction mechanism of nitrogen-doped zinc oxide with atomic layer deposition

Atomistic mechanism for the nitrogen-doped ZnO Atomic Layer Deposition (ALD) on Si(100)-2 × 1 surface is investigated within the framework of density functional theory. We have examined three possible reaction pathways involving the metal precursors diethyl Zinc and ammonia hydride (NH₄OH), which serves as oxidizer and nitrogen doping source. The dissociation of NH₄OH leads to NH₃ and H₂O for latter parallel half reactions occurring simultaneously following the diethyl Zinc half reaction. Our results show overall three reactions are exothermic and energetically favorable, however, the adsorption energy in diethyl Zinc half reaction is only − 6.53 kJ/mol, which is much lower compared to NH₃ and H₂O half reactions, indicating longer zinc precursor pulsing time is indeed needed in order to attain better -ZnCH₂CH₃? group coverage. The energy barrier in NH₃ and H₂O half reactions are 142.00 and 94.16 kJ/mol respectively, combining with the calculation results that the exothermic energy of the H₂O half reaction is 39.04 kJ/mol higher than the NH₃ half reaction, we concluded that in the initial ALD zinc oxide procedure the ZnO deposition rate is much faster than the incorporation of nitrogen, which is in accordance with the function of nitrogen as p-type impurities in ZnO semiconductor.     

Ab initio study of proton dynamics on perovskite oxide surfaces

First-principles studies of the proton dynamics in perovskite oxides and the water adsorption on various oxide surfaces are briefly reviewed. Recent progress in the study of the microscopic mechanism of the proton absorption from perovskite oxide surfaces is also presented. It is shown that dopant ions on the surface and oxygen vacancies in the inside just below the surface play an important role for the proton absorption, while oxygen vacancies on the surface are influential for the dissociative adsorption of water molecules.     

Effect of bias voltage on growth property of Cr-DLC film prepared by linear ion beam deposition technique

Cr-containing diamond-like carbon films were deposited on silicon wafers by a combined linear ion beam and DC magnetron sputtering. The influence of the bias voltage on the growth rate, atomic bond structure, surface topography and mechanical properties of the films were investigated by SEM, XPS, Raman spectroscopy, AFM, and nano-indentation. It was shown that the chromium concentration of the films increased with negative bias voltage and that a carbide phase was detected in the as-deposited films. The surface topography of the films evolved from a rough surface with larger hillocks reducing to form a smoother flat surface as the bias voltage increased from 0 to −200 V. The highest hardness and elastic modulus were obtained at a bias voltage of about −50 V, while the maximum sp³ bonding fraction was acquired at −100 V. It was suggested that the mechanical properties of the films not only depended on the sp³ bonding fraction in the films but also correlated with the influence of Cr doping and ion bombardment.     

Ab initio study of the adsorption of antimony and arsenic on the Si(110) surface

We have performed first principles total energy calculations to investigate the adsorption of Sb and As adatoms on the Si(110) surface using a (2 × 3) supercell. The energetics and atomic structures have been investigated in four atomic configurations. One structure is obtained by placing 1/3 of a monolayer (ML) of Sb (As) atoms on the Si(110) surface. The other three geometries are obtained by depositing 1 ML of Sb (As) atoms on the surface. In the first case the structure is formed by four trimers, in the second case the geometry is formed by zigzag atomic chains and in the third case the structure contains “microfacets”. The energetics results of the Sb adsorption show that for low coverage the tetrahedrons formed by the adsorption of 1/3 ML is the most stable configuration, while in the monolayer region the zigzag atomic chain is the most stable structure. However, the total energies of the trimer and microfacet structures are slightly higher, indicating that under some conditions, they may be formed. In an experimental report it has been suggested that the adsorption of 1/3 and 1 ML of Sb corresponds to the low and high coverage in the experiments of Zotov et al. [A. V. Zotov, V. G. Lifshifts, and A. N. Demidchik, Surf. Sci. 274, L583 (1992)]. On the other hand, our results of the As adsorption show that for low coverage, the tetrahedrons in the adsorption of 1/3 ML also give the most stable configuration. However, at the 1 ML coverage, a structure formed by microfacets is the most stable structure, in agreement with previous results.     

Ab initio simulations of the mechanics and electrical transport of Pt nanowires

Based on first principles, theoretical studies of atomic-scale platinum contacts are presented. A short monatomic wire freely suspended between tips is seen to vibrate as its tensile load increases. The main vibration mode is transversal for lower tensions and longitudinal for higher tensions up to the breaking of the nanowire. The computed conductance exhibits oscillation in the sub-picosecond regime that can be well correlated to the mechanical oscillations of the nanowire. Both the values for the maximum tensile load and the average conductance agree well with available experimental measurements.     

Ab initio tensile testing simulation of aluminum and aluminum nitride ceramics based on density functional theory

The ideal strength and mechanical behavior of aluminum, aluminum nitride, and their composites at zero temperature are investigated using ab initio norm conserving pseudopotential methods based on local density approximation. The total energy and stress of supercells which contain these atomistic models are calculated under uniaxial tensile strain. Estimated various physical properties of aluminum and aluminum nitride at equilibrium state are in good agreement with the experiment. The tensile test of the composite model shows a failure of the composite in the aluminum matrix. The ideal strength of these models is also estimated.     

Electronic structures of relaxed BiOX (X = F, Cl, Br, I) photocatalysts

For photocatalysts BiOX (X = F, Cl, Br, I), the atomic sites have been relaxed and the electronic structures have been calculated via the density functional theory (DFT) with or without the adoption of Bi 5d states. BiOF exhibits a direct band gap while the other three species present the indirect feature. The consideration of Bi 5d states results in apparent expansion of the gaps, which are closer to the experimental results. The transition positions are almost independent of the incorporation of Bi 5d states, and the conduction-band bottom flattens with the increase in X atomic number. Both O 2p and X np (n = 2, 3, 4 and 5 for X = F, Cl, Br and I, respectively) states dominate the valence-bands while Bi 6p states contribute most to the conduction-bands. The density peak of the localized X np states in the valence-band shifts towards the valence-band top with the increasing X atomic number, along with certain changes in the valence and conduction bandwidths. Atomic and bond populations, as well as the spatial distribution of orbital density have also been investigated.     

Methods for mitigating disruptions in complex supply chain structures: a systematic literature review

Supply chain risk management is extremely important for the success of a company. Due to the increasing complexity of supply chains, avoiding and mitigating the effects of disruptions is very challenging. This article presents the results of a systematic literature review and content analysis in order to provide a comprehensive overview of the methods that are currently used for mitigating supply chain disruptions. The results of the review indicate that research in this field is interdisciplinary and that no common modelling language has emerged thus far. Prior research mostly redraws to graph theory and/or social network analysis, although a few methods have been developed recently specifically for supply chain risk management. We observe that prior contributions addressed risk and structure mostly separately and that only a few works focused on their intersection. The results of this review are consolidated in a research agenda that calls for research on the risk-structure-interface and the development of proxy methods.     

DFT studies of sulfur induced stress corrosion cracking in nickel

The sulfur induced embrittlement of nickel Σ 5 (0 1 2), a symmetrical tilt grain boundary, has been studied to understand why and how impurity atoms weaken the grain boundaries of nickel. By using first-principles calculations, the effect of concentration of sulfur has been investigated to comprehend the basic rules on the deterioration of a nickel grain boundary. We have found that the extension of the nickel grain boundary is a result of the repulsion of the segregated and neighboring sulfur atoms.     

Pricing and ordering decisions in a supply chain with imperfect quality items and inspection under buyback of defective items

In this article, the economic production and inventory model in a three-layer supply chain including one distributor, one manufacturer and one retailer for a single-product and general demand functions under three scenarios is developed. We assume that during the production process, both healthy and defective items are generated. As the first scenario, we develop the first model, in which the defective items are not reworked and all considered as scrape, while in the second model, we assume that the defective items are reworked and are sold as perfect item. In the second scenario, we assume that defective item can be sold with lower price than the selling price. Moreover, raw materials with imperfect quality are sent back from a distributor to outside supplier under a lower price. Determining the order quantity of the distributor and the selling prices of the distributor and the manufacturer as well as the retailer was the goal of this article such that the total profit of each member is maximised. In order to solve the models, the Stackelberg approach is employed between the members, and the concavity of the profit functions is proved using several theorems. Then, closed form solutions are derived for the decision variables and a solution algorithm is proposed to determine the optimal solutions. Finally, a numerical example is presented to illustrate the applicability of the model.