Bond Angels Research Articles

Impact of shape and size of particles on the magnetic properties of chromium doped cobalt ferrite

The hydrothermal method was used to synthesize CoCrxFe2−xO4 (x = 0, 0.2, 0.4, 0.6, 0.8 at %) nanoparticles. X-Ray Diffraction (XRD) analysis indicates that nanoparticles have a single-phase spinel structure. The lattice constant (a) was calculated by the Rietveld method through MAUD program. The crystallite size (D), mean ionic radii of A and B sites, bond lengths, interionic bond angels and distances of samples were also calculated. Variation of structural parameters agrees with the cation distribution determined in the magnetic study section. The FESEM images confirmed the data extracted from XRD analysis. The change of particles' shape from spherical to octahedral by Cr doping was also observed. The particles’ size of all the samples was studied by drawing the size distribution plots. It was indicated that the size of ferrite particles was varying in the range of 21–110 nm. Increment of Cr3+ content caused the saturation magnetization to be declined, while the coercive field illustrated an opposite behaviour. The effect of size and shape of particles as well as the cation distribution were key factors employed to justify the magnetic properties of Co–Cr ferrite structures. The novel outcome of this work is that the coercive field of the ferrite samples can be tailored as a parameter for high coercivity-needed applications by the effect of shape and size of particles.

Diffusion behaviors of HF in molten LiF-BeF2 and LiF-NaF-KF eutectics studied by FPMD simulations and electrochemical techniques

The hydrofluorination reaction has proven to be a very effective approach to remove impurities in the preparation and usage of molten LiF-BeF 2 (Flibe) and LiF-NaF-KF (Flinak) eutectic salts, however, the diffusion behaviors of HF in two molten fluorides are incompletely understood. Here we design two systems, HF+Flibe and HF+Flinak, to reveal the diffusion properties and local structures as well as their correlations by first principles molecular dynamics (FPMD) simulations and electrochemical methods . It is shown that the strong interaction between Be 2+ and F – in molten Flibe reduces their diffusivities while providing more space for Li + migration. The diffusion coefficient of H + in molten Flinak is higher than that in molten Flibe determined by the fast exchange of H + between two F anions, and the larger diffusivity of F – in molten Flinak is related to the irregular movement of free F anions. Besides, the quasi-gaseous transport behavior of HF in two molten fluorides is proposed in this study according to the stable H-F bonds. Moreover, the experimental diffusion coefficient of HF in molten Flinak estimated by the method of convolution linear sweep voltammetry is consistent with our simulation value, and the larger diffusivity is well explained by the higher stretching vibration frequency between H + and F – in molten Flinak. Finally, the ionic diffusion coefficients are descripted by the first sharp diffraction peaks of structure factors, the nearest neighbor peaks of radial distribution functions , and the major bond angels of angular distribution functions, and it is speculated from these FPMD simulations that the peak position has a higher weight on diffusion coefficient. Overall, in-depth understandings of the structure-property relationships of HF+Flibe and HF+Flinak systems provide insights into the molten salt purification technology and the daily operation of molten salt reactors .

Structural, electronic and magnetic properties of Mott insulating Y1-xLaxTiO3 from hybrid density functional calculations

The ferromagnetic (FM)-antiferromagnetic (AFM) transition is experimentally observed in Y1-xLaxTiO3. The underlying microscopic mechanism for FM-AFM transition is still an open problem and far from fully understood. Here, structural, electronic and magnetic properties of Mott insulating Y1-xLaxTiO3 with x = 0, 0.25, 0.5, 0.75, and 1 are studied using hybrid density functional method. Y1-xLaxTiO3 stabilizes in an orthogonal perovskite structure. As x increases, the lattice parameters and unit volume almost increase linearly. Y1-xLaxTiO3 is an FM insulator at x = 0 and 0.25, an A-type AFM insulator at x = 0.5 and 0.75, and a G-type AFM insulator at x = 1. A spin-glass behavior is predicted to emerge at 0.25 < x ≤ 0.5. The calculated lattice parameters, band gaps, and magnetic ground states of Y1-xLaxTiO3 are in good agreement with available experimental data. The Ti–O–Ti bond angels increase with increasing x while the total energy difference between the AFM and FM states decreases and then is less than 0 meV. An FM-AFM phase transition is strongly favored with decrease of the GdFeO3-type distortion. The present study reproduces structural, electronic and magnetic properties of Mott insulating Y1-xLaxTiO3, and interprets well experimentally-observed magnetic phase transition.

Molecular modeling analyses for polyvinylidene X (X=F, Cl, Br and I)

Polyvinylidene (PVDF) substituted with different halogens (F, Cl, Br and I) has been studied theoretically by performing some semiempirical calculations at PM3 to obtain some physical parameters and improve the electronic properties. As a result of substitution bond length increases from 1.1083 Ǻ to 1.9921 Ǻ; bond angels decreased from 105.5120° to95.3750°; total dipole moment is increased from 0.0013 to 9.8242 Debye and the energy gap is decreased from 14.2929 to 6.1591eV. In addition, ESP results are indicated that the electro-negativity of the studied model molecules is increased upon substitution. The change in these calculated physical parameters reflects the reactivity of PVD.

Antiradical, antimicrobial and enzyme inhibition evaluation of sulfonamide derived esters; synthesis, X-Ray analysis and DFT studies

Two carboxylate esters (methyl: (I) and ethyl: (II)) of 4-{(4-methylphenylsulfonamido)- methyl}cyclohexanecarboxylic acid (sulfonamide) were synthesized and characterized by FTIR and X-ray crystallography. DFT studies were conducted in order to optimize the structures using Gaussian software which confirmed the bond angels and bond lengths obtained from single crystal analysis. Both Compounds (I and II) were evaluated for their biological studies viz; antioxidant activity (DPPH), enzyme inhibition activity (esterase and proteases), antibacterial (Halomonas halophila, Halomonas salina, Shigella sonnei, Bacillus subtilis, Chromohalobacter salexigens, Chromohalobacter israelensis, Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae) and anti-fungal (Aspergillus niger and Alternaria alternata). Results depicted that II is more active as compared to I in antioxidant and esterases while I is more potent against protease while moderate results were shown by both.

Structural, electronic and spectral properties of carborane-containing boron dipyrromethenes (BODIPYs): A first-principles study

In this work, we reported the geometrical structures, electronic and spectral properties of the carborane-containing BODIPYs complexes using the density functional theory calculations. In two structures, the calculated main bond lengths and bond angels of structural framework are consistent with X-ray experiment, and the two BODIPYs complexes are thermodynamically and kinetically stable. The strongest DOS band is mainly dominated by the BB and BH σ-bonds of carborane fragment, whereas the π-type MOs on the pyrromethene fragment contribute to the high-energy DOS bands. Analysis of the AdNDP chemical bonding indicates that the carborane cage can be stabilized by eleven delocalized 3c2e and two delocalized 4c2e σ-bonds, while the pyrromethene fragment corresponds to five delocalized 3c2e π-bonds. In addition, the main characteristic peaks of the two simulated IR spectra for the BODIPYs complexes are properly assigned. Hopefully, all these results will be helpful for understanding the electronic structures, and further stimulate the study on the biological and medical applications.

Giant Anisotropic Raman Response of Encapsulated Ultrathin Black Phosphorus by Uniaxial Strain

The giant anisotropic Raman response of encapsulated ultrathin black phosphorus (BP) is reported by uniaxial strain. A modified bending technique is employed to apply precise uniaxial tensile strain along the zigzag or armchair direction of the ultrathin BP encapsulated by a layer of polymethyl methacrylate. The Raman shift rates of the A 1 g, B 2g, and A 2 g modes are significantly distinct for strain applied along different directions. For the strain applied along zigzag direction, the Raman shift rate of the B 2g mode can reach a remarkable value of ≈−11 cm−1/% strain. In addition, the Grüneisen parameter is as high as ≈2.5, which is the largest among all the reported common 2D materials. Density functional perturbation theory calculations are performed to understand the exceptional anisotropic strain response discovering that not only the bond lengths but also the bond angels are changed in the strained ultrathin BP, which lead to the giant anisotropic Raman response. Furthermore, an alternative method based entirely on the strained ultrathin BP and nonpolarized Raman spectroscopy is demonstrated to determine the crystallographic orientations of ultrathin BP. This work paves a way to study the strain‐induced anisotropic electrical conductance and magnetotransport properties of BP.

(Invited) Strain Engineering in Ultrathin Black Phosphorus

We report the giant anisotropic strain response in vibrational modes of ultrathin black phosphorus (BP). A modified bending technique was employed to apply precise uniaxial tensile strain to zigzag or armchair directions of the BP flakes. The Raman shift rates of A1 g, B2g and A2 g modes of BP are significantly distinct for strain applied along zigzag or armchair directions. For the applied strain along zigzag direction, the Raman shift rate and the Grüneisen parameter of the B2g mode can reach a remarkable value of ~-11 cm-1/% strain and ~3.7 respectively, which are the largest among all the reported values in two-dimensional materials. The density functional theory calculations were performed to understand the exceptional anisotropic strain response in the vibrational modes of BP. It is found that not only the bond lengths but also the bond angels are changed in BP upon applied strain which lead to giant anisotropic response in mode B2g . Furthermore, we demonstrate a simple method based entirely on the strained BP and conventional Raman spectroscopy to determine the crystallographic orientations of BP without the aid of polarization Raman spectroscopy. This work may pave a way to study the strain-induced anisotropic electrical conductance and the magnetotransport properties of BP.

DFT/NBO study of Nanotube and Calixarene with anti-cancer drug

AbstractNowadays use of calixarenes and nanotubes are widely spread in the pharmaceutical industry. In this work, interaction of between calix[4]arene and nanotube (6, 6) with Fluorouracil drug are investigated. The DFT calculations have been performed using the Gauss view and Gaussian98 in B3LYP method and 6-31G (d) standard basis set at 298.15K. There are calculated length bond (Å), bond angel (deg), dihedral angel (deg), energy hyperconjucation, and total energy (KJ mol-1), moment dipole (Debye), occupancy between nanotube (6, 6) and calix[4]arene with anticancer drug in B3LYP/6-31G (d) method. These cases and medicines show that complex1 is more stable than complex1. The parameter ofE2, gap energy and∆E°in composite of nanotube- Fluorouracil are higher than calix[4]arene-Fluororacil; therefore, complex1is more stable.

Comparison of drug delivery systems: Nanotube and p- Sulphonatocalix[4]arene, by Density Functional Theory

Nowadays, the use of calixarenes and nanotubes are widely spread in the field of drug delivery. In this work, interaction between p-sulphonatocalix[4]arene and nanotube(6,6)with Fluorouracil drug is investigated. Density function theory (DFT) calculations have been performed using the Gauss view and Gaussian03 by B3LYP (beck three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional) method and 6-31G (d) standard basis set. The length bond (Å), bond angel (degree), dihedral angel (in degree), hyperconjucation energy, and total energy (KJ mol-1), formation energy (KJ mol-1), moment dipole (in Debye) and occupancy of between nanotube (6,6) and p-sulphonatocalix[4]arene with anti-cancer drug are calculated by B3LYP/6-31G (d) method. The results show that composite 2 is more stable than the other composite. The hyperconjucation energy (E 2 ) in the p-sulphonatocalix[4]arene-fluorouracil is higher than that in the other composite. The standard formation energy in the the p-sulphonatocalix[4]arene-fluorouracil is more negative value (lower) to composite 1.

Computation of the bond dissociation enthalpies and free energies of hydroxylic antioxidants using the ab initio Hartree–Fock method

IntroductionA new method for calculating theoretical bond dissociation enthalpy (BDE) and bond dissociation free energy (BDFE) of hydroxylic antioxidants is forwarded. BDE and BDFE may be understood as activation energies accompanying the formation of transition states, which may undergo downhill homolytic dissociation. The new method does not involve the complete fission of O–H bonds.MethodTheoretical gas phase BDE values were calculated with the ab initio unrestricted Hartree–Fock (UHF) method, as changes in enthalpy between ground singlet states (GS) and triplet dissociative states (DS). Similarly, gas phase BDFEs were estimated from the corresponding changes in Gibbs free energy. The results were then compared with reliable experimental reports.ResultsThe proposed theoretical approach of BDE and BDFE determination was tested using 10 simple phenols, 5 flavonoids, and l-ascorbic acid derivatives. The agreement between our calculated gas phase results and the adopted experimental values were generally within 0.5 kcal mol−1, with a very few exceptions.DiscussionGenerally, steric interactions as well as intramolecular hydrogen bonding involving the dissociating OH group should be minimized in the GS. The DS are both electronically and vibrationally exited transition states. They have one unpaired electron on the carbon atom, which bears the homolytically dissociating OH group and are second order saddle points with a fixed <C–O–H bond angel of 180°.ConclusionIt was concluded that ab initio UHF was well suited for the estimation of gas phase BDE and BDFE. The method presented has a good potential for application across a range of hydroxylic antioxidants. Currently, work is underway to extend its application in other class of antioxidants.

Efficient, approximate and parallel Hartree–Fock and hybrid DFT calculations. A ‘chain-of-spheres’ algorithm for the Hartree–Fock exchange

In this paper, the possibility is explored to speed up Hartree–Fock and hybrid density functional calculations by forming the Coulomb and exchange parts of the Fock matrix by different approximations. For the Coulomb part the previously introduced Split-RI-J variant (F. Neese, J. Comput. Chem. 24 (2003) 1740) of the well-known ‘density fitting’ approximation is used. The exchange part is formed by semi-numerical integration techniques that are closely related to Friesner’s pioneering pseudo-spectral approach. Our potentially linear scaling realization of this algorithm is called the ‘chain-of-spheres exchange’ (COSX). A combination of semi-numerical integration and density fitting is also proposed. Both Split-RI-J and COSX scale very well with the highest angular momentum in the basis sets. It is shown that for extended basis sets speed-ups of up to two orders of magnitude compared to traditional implementations can be obtained in this way. Total energies are reproduced with an average error of <0.3kcal/mol as determined from extended test calculations with various basis sets on a set of 26 molecules with 20–200 atoms and up to 2000 basis functions. Reaction energies agree to within 0.2kcal/mol (Hartree–Fock) or 0.05kcal/mol (hybrid DFT) with the canonical values. The COSX algorithm parallelizes with a speedup of 8.6 observed for 10 processes. Minimum energy geometries differ by less than 0.3pm in the bond distances and 0.5° in the bond angels from their canonical values. These developments enable highly efficient and accurate self-consistent field calculations including nonlocal Hartree–Fock exchange for large molecules. In combination with the RI-MP2 method and large basis sets, second-order many body perturbation energies can be obtained for medium sized molecules with unprecedented efficiency. The algorithms are implemented into the ORCA electronic structure system.

Influence of the stress on the transport behavior of La0.83Sr0.17MnO3 film

The LSMO (x=0.17) film on the Si (111) substrate was fabricated by the sol-gel m ethod.The R-T curves, the infrared spectra and XRD results of the block and the film with different thickness show that the crystals of the LSMO films are orth ogonal, and the film orientation has some relation with the film thickness. Whe n the film thickness lies between the 450nm to 680 nm, the orientation is 〈200 〉, but when the film thickness equals to 900 nm, the orientation is 〈020〉. Ac cording to the reactive energy and the harmonic oscillator model, the relational expressions, between the infrared absorption and the Mn-O-Mn bond length and bo nd angel were studied. The infrared absorption near 600cm-1 relates t o the different lattice constant b, and the metal-insulator transformation tempe ratures (TMI) of the block material and the films differ much, those of the films being much lower than that of the block material and, at the same time, has something to do with the film thickness. The paper indicates that the stress in the LSMO films inducing the lattice constant change and then arousing the change of bond angel and JT effect is the main reason for the change of the transformation temperature.

CORE LEVEL CHEMICAL SHIFTS AND LINE SHAPES FOR SYSTEMS WITH DIFFERENT VALENCIES AND Cu-O NETWORKS

We have studied the Cu -2p core level photoemission spectrum of a variety of cuprates, mainly focusing on the chemical shift and the shape of the leading peak. The spectra are calculated using the Anderson impurity model and we obtain a very good agreement with the experimental data. We find that the shape of the leading peak depends crucially on the structure of the Cu - O network. The main peak turns out to be quite narrow if the network consists of Cu - O - Cu bond angels of the order of 90°. On the other hand, if the Cu - O atoms are arranged with bond angles of approximately 180°, the main peak becomes substantially broader and contains a rather complicated structure. However, in some cases it is not sufficient only to consider the Cu - O network because interactions with other atoms are also important. In the model compounds Cu 2 O , CuO and NaCuO 2, where Cu is formally monovalent, divalent and trivalent, respectively, we find that the number of 3d electrons is rather similar. Nevertheless, the binding energy increases with the valence as expected from chemical intuition. The spectra exhibit a large variation in the strength of the d9-like satellite and in the width of the main line. We, furthermore, study the chemical shift of three inequivalent Cu atoms in YBa 2 Cu 3 O 6.5, and compare the results with the model compounds, which suggests that the different Cu atoms in YBa 2 Cu 3 O 6.5 have formal valences of approximately one, two and three. These findings are analyzed and related to the formal valence.

Microstructure and X-ray analysis on LaCaMnO thin film

La 2/3Ca 1/3MnO 3 thin films in the thickness range between 40–500 nm, have been deposited by an optimised pulsed laser deposition process on SrTiO 3 (STO) single crystal substrates. The surface morphology of the thin films was examined by AFM and SEM. X-ray investigations were applied to study the lattice parameters. XRD pole figures show an epitaxial growth of manganite thin films on (100) STO substrate. According to X-ray diffraction pattern, we could derive the dependence of the lattice parameters within the thickness of the film. It is shown that Rietveld refinement of XRD pattern is essential to assess the structure of the manganite phase. Lattice parameters are refined and distances and bond angels were determined. A correlation between structure, transport properties and thickness are discussed.

Calibration of effective van der Waals atomic contact radii for proteins and peptides.

Effective van der Waals radii were calibrated in such a way that molecular models built from standard bond lengths and bond angles reproduced the amino acid conformations observed by crystallography in proteins and peptides. The calibrations were based on the comparison of the Ramachandran plots prepared from high-resolution X-ray data of proteins and peptides with the allowed phi, psi torsional angle space for the dipeptide molecular models. The calibrated radii are useful as criteria with which to filter energetically improbable conformations in molecular modeling studies of proteins and peptides.

Molecular structural of the gauche and trans conformers of ethylamine as studies by gas electron diffraction

The geometrical parameters for the two conformers, gauche ( g) and trans ( t), of ethylamine have been determined by a joint analysis of the electron diffraction intensity measured in the present study and the rotational constants reported in the literature. The optimized geometries estimated by an SCF MO calculation with a 4-31G(N*) basis set were also used in the analysis to complement the experimental data. The bond lengths ( r g) and the bond angels ( r z ) determined are r(CH) av = 1.107(6) Å r(CN) t = 1. 470(10)Å, r(CN) g = 1.475(10) Å r(CC) t = 1.531(6) Å r (CC) g = 1.524(6) Å , ∠CCN) t = 115.0(3)°, and ∠CCCN g = 109.7(3)°. The uncertainties represent estimated limits of error. The difference between the CCN g and CCN g angles predicted by a previous ab initio calculation is confirmed. The enthalpy difference,Δ H( g t), is determined to be 306(200) cal mol −1 using the abundance of the trans conformer, 46(10)%.

Exchange interactions in tetranuclear copper(II) complexes

A good description of the exchange effect from the experimental point of view is only possible using relatively simple systems. The two spin case ( e.g. Cu(II)) is the simplest one, nevertheless it also poses a number of problems. If more than two paramagnetic centres are coupled, then the problems become even more complicated. On the other hand when one has more than two centres, the chances of transferring the linear case to a three-dimensional case are increased. The latter case is far more important for the problems in question. In copper(II) the number of centres are equal to 4 and thus one of the possible molecular shapes is the tetranuclear cuban-like type. The main part of the contribution is concentrated around our present knowledge of the exchange effect in this type of tetranuclear Cu(II) complex. The exchange pathway runs along the diamagnetic bridge ligands. When one considers the lowest symmetry case C 1, 6 different exchange integrals for describing the exchange effect are required. The simplest description still needs two independent integrals. In principle, the tetranuclear cuban type structures can be divided in to two different types. Type I forms a tetrameric unit, consisting of two weakly coupled Cu 2O 2 dimers. The coupling occurs perpendicular to the plane of the ring. Type II can be derived from a boat like eight membered Cu 4O 4 ring. In the case of the former type of structure there is an overall antiferromagnetic effect and in the latter type one finds an overall ferromagnetism. There is a continuous series of examples verified between the two types in the groups of aminoalcohol or iminoalcohol ligands. The greatest point of interest at present is the question of which geometrical factors (bond lenghts, bond angels) determined the strength and the sign of the exchange effect. These relationships for the tetrameric cuban type clusters known up to the present time are presented. Moreover, the strength and the sign of the exchange integrals depends also on the type of ligands near the paramagnetic centre, e.g. saturated or unsaturated groups. This relates to the fact that the energy level of each paramagnetic center depends upon its chemical surrounding. In this contribution we present examples which can explain the relation between the changes in the chemical structure and the strength of the exchange effect. A good example is the change of the molecular structure and also the exchange integrals under the influence of different solvents. This relates to the fact that the different interaction energies between the exchange coupled molecule and the solvent cause different modifications with different magnetic behavior. The aims of this contribution is to explain these small effects.