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In this paper, the structures and properties of (HF)nH2O (n = 1–9) clusters are studied by the combination of genetic algorithm (GA) and density functional theory(GDF) method. The structures are optimized at B3LYP/6–311++G(d,p) level. The refined energies are computed at CCSD(t)/aug-cc-pVDZ level. Infrared spectrum analysis, charge analysis, orbital analysis, and stability analysis are performed on the most stable configurations of each size. Lower-lying structures are obtained for (HF)nH2O (n = 5,6) clusters. (HF)7H2O cluster has special ability based on stability analysis. NCI analysis is conducted on the global optimal structure of all size clusters, and it is found that there are obvious hydrogen bonds in the clusters. Hydrogen bonding is an important factor in stabilizing (HF)nH2O (n = 1–9) composite clusters. The studied clusters can be divided into two categories: non-ionic clusters (HF)nH2O (n = 1–5) and ionic clusters (n = 6–9). [ABSTRACT FROM AUTHOR]

The Cu−O−Cu core has been proposed as a potential site for methane oxidation in particulate methane monooxygenase. In this work, we used density functional theory (DFT) to design a mixed‐valent CuIII−O−CuII species from an experimentally known peroxo‐dicopper complex supported by N‐donor ligands containing phenolic groups. We found that the transfer of two‐protons and two‐electrons from phenolic groups to peroxo‐dicopper core takes place, which results to the formation of a bis‐μ‐hydroxo‐dicopper core. The bis‐μ‐hydroxo‐dicopper core converts to a mixed‐valent CuIII−O−CuII core with the removal of a water molecule. The orbital and spin density analyses unravel the mixed‐valent nature of CuIII−O−CuII. We further investigated the reactivity of this mixed‐valent core for aliphatic C−H hydroxylation. Our study unveiled that mixed‐valent CuIII−O−CuII core follows a hydrogen atom transfer mechanism for C−H activation. An in‐situ generated water molecule plays an important role in C−H hydroxylation by acting as a proton transfer bridge between carbon and oxygen. Furthermore, to assess the relevance of a mixed‐valent CuIII−O−CuII core, we investigated aliphatic C−H activation by a symmetrical CuII−O−CuII core. DFT results show that the mixed‐valent CuIII−O−CuII core is more reactive toward the C−H bond than the symmetrical CuII−O−CuII core. [ABSTRACT FROM AUTHOR]

Boron‐based compounds such as frustrated Lewis pairs and borylenes that mimic transition‐metal(TM)‐like reactivity have attracted significant interest in recent years. This work examines the reactivity of boron oxide (B2O3) towards dioxygen for methane activation. Density functional theory in combination with orbital analysis were utilized to derive mechanistic pathways for methane‐to‐formaldehyde conversion over B2O3 in presence of closed‐shell singlet and triplet O2. Multiple pathways were screened on the triplet spin state. Best route via the triplet spin state depicts the interaction of B2O3 with dioxygen (O1=O2) and CH4 at a barrier of 49.8 kcal mol−1, to produce an intermediate having a B−O1−O2H unit and a free CH3 radical, which later react together at a barrier of 57.6 kcal mol−1, to finally yield HCHO. In the singlet spin state, a free CH3 radical does not form instead an intermediate with a B−O1−O2−CH3 unit is found after crossing a barrier of 41.1 kcal mol−1, which further undergoes via a relatively lower barrier of 23.4 kcal mol−1 to yield HCHO. Thus, the singlet pathway is energetically preferred over the triplet one. Orbitals further capture that at singlet and triplet states, methane activation follows a hydride and a hydrogen‐atom‐transfer mechanism, respectively. [ABSTRACT FROM AUTHOR]

Context: The structures of Ag2n-1Sn− (n = 2–11) clusters are obtained by the combination of genetic algorithm (GA) and density functional theory (DFT). All the global minimum structures prefer hollow polyhedral structures, in which S–Ag-S element, triangular Ag3S3 and tetragonal Ag4S4 units present to stabilize the structures. The S atoms in the structures appear in μ3-S or μ4-S form. Adiabatic and vertical electron affinities of the clusters have been obtained, which reveals that they increases as cluster size. Stability analysis shows that Ag9S5− and Ag19S10− have special stability. The HOMO, LUMO orbitals of the clusters are obtained and the orbital components of them are calculated. The HOMO orbitals are mainly from the p orbitals of S atoms, whereas the s, p and d orbitals of Ag atoms contribute much bigger than the p orbitals of S atoms for LUMO orbitals. The orbital delocalization indexes (ODI) of the HOMOs and LUMOs are calculated, and the small ODIs of the HOMOs and LUMOs for n = 4–10 reveal that these orbitals are highly delocalized. By studying the projected density of states and molecular orbitals of Ag9S5− and Ag19S10− clusters, it is found that their molecular orbitals have superatomic properties. Superatomic properties play an important role in stabilizing clusters. Methods: This work used combined genetic algorithm and density functional theory (GA-DFT), and PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) method to optimize the structures. Gaussian 16 program, Gauss view 6.0.16 program and Multiwfn 3.8 code are the softwares used. [ABSTRACT FROM AUTHOR]

Abstract Nanosatellite missions represent a promising option for the exploration of the near-Earth asteroid population since they provide low-cost versatile platforms for scientific observations. This paper describes the preliminary orbital and navigation analyses for the DustCube mission, which was pre-selected to reach the binary asteroid system Didymos on-board ESA's AIM spacecraft. Possible candidate orbits that exploit the binary nature of the system are identified and traded off to produce a preliminary concept of operations. The overall feasibility of the proposed scenario is then addressed by integrating the spacecraft trajectories in a realistic dynamical environment, evaluating their sensitivity to state errors, and estimating the accuracy of the orbit determination system. Preliminary results suggest that autonomous navigation of a Cubesat platform within a binary asteroid system is technically feasible. The proposed solution, which combines an initial parking orbit at the L 4 equilibrium point with a Distant Retrograde Orbit for proximity operations, is shown to be consistent with the estimated orbit determination accuracy and allows to fulfil the mission requirements. [ABSTRACT FROM AUTHOR]

We study observations of a fireball that occurred in Kylmälä, Finland with the aim of determining its Keplerian orbital elements. The fb_entry program is used to determine the fireball's trajectory based on the observations. The orbit is then determined using this trajectory as the input parameters with the Meteor Toolkit software. We successfully determine the fireball's orbit, which appears to be an ordinary near-Earth asteroid orbit. We find that the fireball's semi-major axis is 1.94 AU, which corresponds to the inner edge of the main asteroid belt and gives cause to suspect that the object originated in the main belt and evolved into a NEA due to the effect of the secular v6 resonance. Several related bodies were also identified. [ABSTRACT FROM AUTHOR]

Fault detection in induction motors is an important task in industry when production greatly depends of the functioning of the machine. This paper presents a new computational model for detecting misalignment and unbalance problems in electrical induction motors. Through orbital analysis and signal vibrations, unbalance and misalignment motor faults can be mapped into patterns, which are processed by a classifier: the Steinbuch Lernmatrix. This associative memory has been widely used as classifier in the pattern recognition field. A modification of the Lernmatrix is proposed in order to process real valued data and improve the efficiency and performance of the classifier. Experimental patterns obtained from induction motors in real situations and with a certain level of unbalance or misalignment were processed by the proposed model. Classification results obtained in an experimental phase indicate a good performance of the associative memory, providing an alternative way for recognizing induction motor faults. [ABSTRACT FROM AUTHOR]

Abstract: We present a theoretical study of the structural response of model water monolayers on a Pd(111) surface upon various electrochemical conditions. Whereas the water molecules pointing toward the vacuum are mostly electrochemically inactive, those lying parallel to the surface undergo an oxidative adsorption under oxidizing conditions, and those pointing toward the surface show a reductive adsorption under reducing conditions. The oxidative adsorption is shown to result from the interaction of the H2O 1b1 orbital with the metal surface dz2 band which becomes bonding only under oxidative conditions. The reductive adsorption arises from the interaction of the H2O 4a1–2b2 orbitals with the dz2 band of the Pd surface. This electronic analysis of electrochemical effects is further validated using the Fukui function associated with the water monolayers. The Fukui function is shown to be a powerful tool for studying electrochemical effects as it is directly linked with the electrochemical bond reorganization and other parameters like the surface capacitance. The electrochemical stability diagram for these water monolayers is computed using a new correction for the DFT electrochemical calculations and compared to previous results. The phase transformation from a positively charge H-up to a negatively charged H-down phase is here confirmed with, however, a potential shifted up to 4.5V compared to our previous report (4.3V). The neutral phase is found to consist in a positively charged H-up phase and a negatively charged H-down phase. This phenomenon is confirmed by large super-cell calculations with different ratio of H-up and H-down phases. The stability of the mixed charged phases is then rationalized in terms of an electrochemical disproportionation whose origin and consequences are further discussed in regards to the results previously obtained on the basis of the ice rules. [Copyright &y& Elsevier]

Abstract: The crystal and electronic structure of Tl2Ni3S2 is investigated by X-ray structure determination and DFT calculations. The question of charges and possible mixed valences of two different Tl positions in Tl2Ni3S2 is discussed with respect to crystal and electronic structure arguments. Crystal structure parameters were redetermined from single crystal data. A relation is given to typical Tl states in reference compounds like mixed valent Tl2S2, high-pressure TlS, LiTl, and ThCr2Si2 type TlNi2S2. This allows for a comparison of different Tl sites with respect to atomic distances, coordinations, valence, charge, and bonding as well as charge redistribution within layered Ni–S substructures. Complementary methods of charge determination from theory are applied as orbital analysis from precise full potential calculations and charge density analysis by zero flux surface integration according to the AIM theory. [Copyright &y& Elsevier]

Abstract: Interest in the deployment of tethered satellites has led to a need for preliminary orbit determination methods which are capable of distinguishing tethered satellites from untethered ones. Classical preliminary orbit determination methods, which are used for Keplerian satellites, generally require two or more position vectors along with their respective observation times in order to determine a preliminary orbital element set. These conventional methods, however, are unable to distinguish between Keplerian and tethered satellites, whose motion is modified due to the presence of a tether force. The use of conventional methods result in the calculation of inaccurate orbital elements if the observed satellite is part of a tethered satellite system. Modifications have been made to four classical preliminary orbit determination methods in order to allow for the identification of tethered satellites. These modifications provide the ability to distinguish between a tethered satellite and an untethered one. This paper applies these modified preliminary orbit determination methods to the problem of the identification of a tethered satellite. The performance of these methods is evaluated through scenarios of differing tether lengths and levels of observation error, and results are compared in order to determine the most accurate method. [Copyright &y& Elsevier]

The electronic structure of Be (II), Mg (II), and Zn (II) acetylacetonates and hexafluoroacetylacetonates was calculated in the DFT approximation. The energies of MOs and ionization energies calculated by the OVGF method were compared with the published data of photoelectron spectroscopy (HeI). The outer valence region of the spectra is equally effectively reproduced by DFT and OVGF methods. The calculations allowed determining the ionization energies of the π 2 orbitals of the chelate cycles. It was determined that an increase in the binding energy of the electrons of the valence and core levels upon substitution of CH 3 >CF 3 by 1,7–2,1 eV was correlated with a change of the negative charge of the carbon atom of the substituted groups on positive one. The polarity of M − O bonds increases in the series of Be, Mg, Zn. It was found that in addition to outer valence orbitals, a covalent bonding was also significantly affected by the deep valence σ-orbital 4 a 1 with a high degree of overlap with metal s-orbitals. • The DFT and OVGF calculations were performed to determine the electronic structure of compounds. • The effect of CH 3 >CF 3 substitution on electronic structure has been studied. • Calculated geometry data and outer valence electronic structure were compared with experimental data. [ABSTRACT FROM AUTHOR]