Boron nitride nanotubes with quadrangular cross sections: Density functional studies

Density functional theory (DFT) calculations have been performed to investigate the availabilities and properties of boron nitride nanotubes (BNNTs) with quadrangular cross sections. To achieve the purposes, the original structure of a representative BNNT was individually decorated by the carbon and silicon atoms to make the C-BNNT and Si-BNNT models. The sp³ hybridizations were set for the C and Si atoms to make possible the formation of the quadrangular cross sections for the BNNTs. The optimized results indicated that the investigated models could be stabilized; however, they showed different properties. The atomic scale properties based on computations of quadrupole coupling constants (C_Q) also approved different properties for the C-BNNT and Si-BNNT models. Moreover, the C_Q parameters indicated that the properties of C-BNNT could be considered similar to the original BNNT; however, more discrepancies were observed for the Si-BNNT.     

Structural and electronic properties of pyrrolidine-functionalized [60]fullerenes

We have investigated energetic, geometric, electronic, and field emission properties of three recently synthesized fulleropyrrolidines based on the density functional theory method B3LYP/6-31G(d). Fulleropyrrolidines show higher conductivity, and solubility in water, and smaller work function in comparison with the pristine C₆₀ fullerene. The functionalization of C₆₀ with different pyrrolidines containing 3NH₂, NO, or NO₂ groups transforms it to an n-type semiconductor. The functionalization can also dramatically enhance the electrophilicity of the C₆₀ about 23–37%. Moreover, it should be mentioned that the work function is mainly influenced by the pyrrolidine containing 3NO₂ group whereas the conductivity is largely affected by the one containing 3NH₂ functionality.     

DFT study of structural,electronic and elastic properties of two polymorphs of monoclinic CsGaQ2 (Q = S,Se)

In this paper, we report an ab-initio calculations of the structural, electronic and elastic properties of monoclinic CsGaQ₂ (Q?=?S, Se) crystals in two polymorphs CsGaQ₂-mC64 and CsGaQ₂-mC16 (Q?=?S, Se). The investigation is done using the pseudo-potential plane-wave (PP-PW) method combined to the generalized gradient approximation (GGA) within the density functional theory (DFT). The calculated equilibrium lattice constants (a, b and c), angle β are in good agreement with the available experimental data. We have calculated and analyzed the energy gap, band structure and density of states. The electronic structure calculation demonstrates that crystals are direct-gap semiconductors. The single-crystal elastic constants C_ij of CsGaQ₂-mC16 are predicted, for the first time, using the stress–strain method. The polycrystalline bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio?ν, and elastic anisotropy A^U are determined based on the predicted C_ij. Our results indicate that CsGaQ₂ (Q?=?S, Se) can be classified as brittle materials.     

Tuning the electronic properties of the fullerene C<Subscript>20</Subscript> cage via silicon impurities

The fullerene C₂₀ represents one of the most active classes of nanostructures, and they have been widely used as active materials for important applications. In this study, we investigate and discuss the tuning of the electronic properties of the fullerene C₂₀ cage via various consternations and locations of silicon atoms. All calculations are based on the density functional theory (DFT) at the B3LYP/3-21G level through the Gaussian 09W program package. The optimized structures, density of state (DOS) analysis, total energies, dipole moments, HOMO energies, Fermi level energies, LUMO energies, energy gaps, and the work functions were performed and discussed. Our results show that the electronic properties of C₂₀ cage do not only depend on the silicon impurity concentrations, but also depend on the geometrical pattern of silicon impurities in the C₂₀ cage. The tuning of the electronic properties leads to significant changes in the charge transport and the absorption spectra for C₂₀ cage via engineering the energy gap. So, we suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of C₂₀ cage for using these structures in nanoelectronics and solar cell applications.     

An Ab Initio Study of the Structural and Electronic Properties of the Low-Defect TiC(110) Surface Simulating Oxygen Adsorption after Exposure to Laser Plasma

An ab initio simulation of the adsorption of atomic oxygen on the low-defect titanium carbide (110) surface reconstructed by laser radiation was performed. The relaxed atomic structures of the (110) surface of the O/Ti _x C _y system with Ti and C vacancies observed during the thermal treatment were studied in terms of the density functional theory. DFT calculations of their structural, thermodynamic, and electronic properties were performed. The bond lengths and adsorption energies were determined for various reconstructions of the atomic structure of the O/Ti _x C _y (110) surface. The effects of the oxygen adatom on the band and electronic spectra of the O/Ti _x C _y (110) surface were studied. The effective charges on the titanium and carbon atoms surrounding the oxygen atom in various reconstructions were determined. The charge transfer from titanium to oxygen and carbon atoms was found, which is determined by the reconstruction of the local atomic and electronic structures and correlates with chemisorption processes. The potential mechanisms of laser nanostructuring of the titanium carbide surface were suggested.     

异质富勒烯C19M(M=Cr,Mo,W)的结构和电子性质的计算研究

采用密度泛函理论(DFT)中的B3LYP方法, 在LANL2DZ基组水平上, 优化了C₁₉M(M=Cr,Mo,W)团簇的几何结构, 得出了它们的基态构型, 并研究了基态结构的物理化学性能.结果表明: 不同的M原子替换后, C₁₉M的动力学稳定性相差不大, 而热力学稳定性随着M原子序数的增加而逐渐升高; 通过对C₁₉M的前线轨道分析发现, M原子对各个轨道均有一定的贡献, M原子对各个轨道的贡献大致随着M原子序数的增加而增加, C₁₉M中金属原子M(M=Cr,Mo,W)上集中了大量的正电荷; C₁₉M的芳香性随着M原子序数的增加而减弱.     

Elastic, electronic, and optical properties of hypothetical SnNNi3 and CuNNi3 in comparison with superconducting ZnNNi3

The elastic, electronic, and optical properties of MNNi₃ (M=Zn, Sn, and Cu) have been calculated using the plane-wave ultrasoft pseudopotential technique, which is based on the first-principle density functional theory (DFT) with generalized gradient approximation (GGA). The optimized lattice parameters, independent elastic constants (C₁₁, C₁₂, and C₄₄), bulk modulus B, compressibility K, shear modulus G, and Poisson's ratio υ, as well as the band structures, total and atom projected densities of states and finally the optical properties of MNNi₃ have been evaluated and discussed. The electronic band structures of the two hypothetical compounds show metallic behavior just like the superconducting ZnNNi₃. Using band structures, the origin of features that appear in different optical properties of all the three compounds has been discussed. The large reflectivity of the predicted compounds in the low energy region might be useful in good candidate materials for coating to avoid solar heating.     

Synthesis,structure, spectroscopic (FT-IR) and density functional modelling studies of 1-[(4-ethoxyphenylimino)methyl]napthalene-2-ol

Synthesis, crystallographic characterisation, spectroscopic (Fourier transform infrared spectroscopy [FT-IR]) and density functional modelling studies of the Schiff base 1-[(4-ethoxyphenylimino)methyl]napthalene-2-ol (C₁₉H₁₇NO₂) have been reported. The molecular structure obtained from X-ray single-crystal analysis of the investigated compound in the ground state has been compared using Hartree–Fock and density functional theory (DFT) with the 6-311++G(d,p) basis set. In addition to the optimised geometrical structures, atomic charges, molecular electrostatic potential, natural bond orbital, non-linear optical (NLO) effects and thermodynamic properties of the compound have been investigated by using DFT. The experimental (FT-IR) and calculated vibrational frequencies (using DFT) of the title compound have been compared. The solvent effect was also investigated for obtained molecular energies and the atomic charge distributions of the compound. There exists a good correlation between experimental and theoretical data for enol-imine form of the compound. The total molecular dipole moment (µ), linear polarisability (α), and the first-order hyperpolarisability (β) were predicted by the B3LYP method with different basis sets 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) 150 and 6-311++G(d,p) for investigating the effects of basis sets on the NLO properties. Our computational results yield that β_tot for the title compound is greater than those of urea.     

Molecular structure, spectroscopic properties and DFT calculations of 2-(methylthio)nicotinic acid

The analyses of possible conformations, molecular structures, vibrational and electronic properties of 2-(methylthio)nicotinic acid molecule, C₇H₇NO₂S, with the synonym 2-(methylsulfanyl)nicotinic acid have been first presented theoretically. At the same time, FT-IR and micro-Raman spectra of 2-(methylthio)nicotinic acid were recorded in the regions 400–4000 cm^?1 and 100–4000 cm^?1, respectively. In our calculations, the DFTB3LYP method with 6–311G(d, p) basis set was used to have the structural and spectroscopic data about the mentioned molecule in the ground state and the results obtained were compared with experimental values. Furthermore, gauge invariant atomic orbital (GIAO) ¹H and ¹³C NMR chemical shifts in different solvents, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-2, HOMO-1, HOMO), lowest unoccupied molecular orbital (LUMO), molecular electrostatic potantial (MEP) surface, atomic charges and thermodynamic properties of molecule have been theoretically verified and simulated at the mentioned level. The energetic behavior of title molecule in different solvent media was investigated by using DFT/B3LYP method with 6–311G(d, p) basis set in terms of integral equation formalism polarizable continuum model (IEFPCM). In addition, the calculated infrared intensities, Raman activities, reduce masses and force constants of the compound under study have been also reported.     

Reaction products from a discharge of N2 and H2S: The microwave spectrum of two conformers of sulfur diimide (HNSNH)

The rotational spectra of two conformations of sulfur diimide (HNSNH) are reported. The HNSNH species are produced in a low-pressure microwave discharge of N₂ and H₂S. The microwave spectrum of the normal isotopic form, HNSNH, and dideutro form, DNSND, of the cis,trans and cis,cis forms have been observed. The electric dipole moment components of both forms have been determined. The molecular structures were determined from the experimental rotational constants and from geometry optimized ab initio calculations with 4-31G Gaussian basis sets and CEP-31G basis sets including polarization. The experimentally and theoretically derived molecular properties are found to be in good agreement.     

Coverage effects under atomic chemisorption: Morse-potential modeling based on bond-order conservation

Our recent analytical Morse-potential model based on bond-order conservation has been extended to treat coverage (θ) effects on the heat of atomic chemisorption Q. For highly symmetric surfaces such as fcc(111), fcc(100), and bcc(100), explicit expressions for Q versus θ have been obtained projecting regularities of Q(θ) and of the overlayer structures, in encouraging agreement with experiment. In particular, the model predicts that Q should typically decrease with θ (though at very low θ, Q can sometimes increase) and that there may be some critical coverage θ_c<1 beyond which the second-order phase transition (hollow→bridge or on-top) will occur.     

Orientational disorder and geometrical isomeric effect on nonlinear optical properties of poly bis(glycine)cadmium chloride

Poly bis(glycine)cadmium chloride (BGCC) crystals of both undoped and doped with thiourea (Tu) were grown from saturated solutions by a slow evaporation technique. The geometrical isomerism of the octahedral BGCC molecule is investigated using single crystal XRD, powder XRD and FT-IR. The significant difference between the two isomers namely facial (fac) and meridional (mer), is explained in terms of the different point group symmetries of C₃ and C₁, respectively. The loss of point group symmetry from C₃ to C₁ is attributed for the observed powder second-harmonic generation (SHG). Semi-empirical calculations from the optimized geometrical parameters also supported non-linear optical properties of the material.     

Modifying a graphene layer by a thymine or a uracil nucleobase: DFT studies

The hybridizations of a graphene layer by a thymine and a uracil nucleobase have been investigated by performing density functional theory (DFT) calculations. The isolated and hybrid structures have been firstly stabilized to reach the minimum energy and the electronic properties have been subsequently evaluated for the optimized structures. The structural and atomic scale parameters indicated that the tip of graphene is important in determining the properties of new hybrids. Moreover, different effects of thymine and uracil nucleobases have been identified in the hybrid structures. Quadrupole coupling constants have been evaluated to characterize the atomic scale properties, in which the most notable effects of hybridizations have been observed for the atoms close to the linking regions whereas negligible effects have been seen for other atoms.     

Structural,electronic and magnetic properties of C59Ir,C58Ir2, and C69Ir heterofullerene nano-cages: first principles study

We studied the structural, electronic, and magnetic properties of C₅₉Ir, C₅₈Ir_2, and C₆₉Ir heterofullerenes by employing density functional theory and the generalized gradient approximation. There are six distinct isomers of C₅₈Ir₂ with high probability to form stable structures. The most stable structure of the C₆₉Ir heterofullerene was investigated by comparing the iridium binding energies at the different atomic sites on the D5h C₇₀ cage. There is a strong hybridization between the atomic orbitals of the iridium and those of the carbon atoms, leading to the spin quenching of the iridium atoms in the most stable C₅₈Ir₂ heterofullerene.     

A cytosine-assisted carbon nanotubes junction: DFT studies

Since nucleobase-functionalized carbon nanotubes (CNTs) are important in the biological applications; the junction of a pair of CNTs through a bridging cytosine linkage is investigated based on density functional theory (DFT) calculations. In the exact model of study, the CNTs are bound to N₁ and C₅ atomic sites of cytosine to make possible the CNT–cytosine–CNT model. To systematically investigate the purpose, the models of original CNT, original cytosine, and primary models of cytosine–CNT in which one CNT is only bound to N₁ or C₅ atomic site of cytosine are also considered. The results of dipole moments and binding energies indicated that the CNT–cytosine–CNT model is the most stable one among all three possible models cytosine-functionalized CNT. The values of energy gaps indicated that the conducting properties of primary cytosine–CNT models are not changed referring to the original CNT but better conductivity could be observed for the CNT–cytosine–CNT model. The values of evaluated quadrupole coupling constants indicated that the electronic densities of nitrogen and oxygen atoms of cytosine detect notable affects during the functionalization processes by the zigzag CNTs and the oxygen atom of CNT–cytosine–CNT model could be proposed as the most proper interacting site of cytosine among other functionalized zigzag models and also the original cytosine. However, the changes of quadrupole coupling constants for the atoms of cytosine are almost negligible during the functionalization processes by the armchair CNTs.     

On the feasibility to study inverse proximity effect in a single S/F bilayer by Polarized Neutron Reflectometry

Here we report on a feasibility study aiming to explore the potential of Polarized Neutron Reflectometry (PNR) for detecting the inverse proximity effect in a single superconducting/ferromagnetic bilayer. Experiments, conducted on the V (40 nm)/Fe (1 nm) S/F bilayer, have shown that experimental spin asymmetry measured at T = 0.5T _C is shifted towards higher Q values compared to the curve measured at T = 1.5T _C . Such a shift can be described by the appearance in superconducting vanadium of magnetic sublayer with a thickness of 7 nm and a magnetization of +0.8 kG.     

Ab initio electronic structure,bonding and optical properties of two relatively new ceramics Hf2Al3C4 and Hf3Al3C5: A comparative study

The structural, electronic and optical properties of the ternary carbides Hf₂Al₃C₄ and Hf₃Al₃C₅ are studied via first principles orthogonalized linear combination of atomic orbitals (OLCAO) method. Results on crystal structure, interatomic bonding, band structure, total and partial density of states (DOS), localization index (LI), effective charge (Q*), bond order (BO), dielectric function (ε), optical conductivity (σ) and electron energy loss function are presented and discussed in detail. The band structure plots show the conducting nature of Hf₂Al₃C₄ and Hf₃Al₃C₅ carbides. DOS results disclose that the total number of states at Fermi level N(E_F) are 1.89 and 2.38 states/(eV unit cell) for Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively. The Q* calculations show an average charge transfer of 0.723 and 0.711 electrons from Hf and 0.809 and 0.807 electrons from Al to C sites in Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively. The BO results provide the dominating role of Al–C bonds with BO value of 6.62 (BO%?=?59%) and 6.66 (BO%?=?49%) for Hf₂Al₃C₄ and Hf₃Al₃C₅ respectively and are considered responsible for the crystals cohesion. The LI results reflect the presence of highly delocalized states in the vicinity of the Fermi level. The dielectric function plots of the real (?₁(?ω)) and imaginary (?₂(?ω)) parts show the anisotropic behavior of Hf₂Al₃C₄ and Hf₃Al₃C₅. The results on optical conductivity (σ) support the trends observed in dielectric functions. The electron energy loss functions reveal the presence of sharp peaks both in ab-plane and along c-axis around 20?eV in Hf₂Al₃C₄ and Hf₃Al₃C₅ ternary carbides.     

定域密度泛函理论对金刚石(100)面再构的研究

用定域密度泛函理论和数值基的方法,进行电荷自洽的总能计算。采用一个集团模型(C₄₉H₃₆)模拟C(100)表面,研究其再构的情况。根据表面原子上受力的计算,得到优化的表面碳原子的几何结构、表面碳原子成对二聚化的成键性质、优化键长(1.415?),以及相应的电子能态结构、表面态的分布等性质。     

Critical behaviour of Ho 2 Fe 17 − x Mn x —magnetisation and Mössbauer spectroscopy

The magnetic properties of Ho₂Fe_17???xMn_x compounds (x = 0–2) of ferromagnetic ordering temperatures up to T_C ~344 K have been investigated by DC magnetization and Mössbauer effect measurements. The nature of the magnetic phase transitions and the critical behaviour around T_C has been investigated by analysis of the magnetisation data and the critical exponents β, γ and δ determined. The critical exponents are found to be similar to the theoretical values of the mean-field model for which β?=?0.5 and γ?=?1.0, indicating the existence of a long-range ferromagnetic interactions. The isothermal entropy changes ΔS around T_C have been determined as a function of temperature in different magnetic fields.     

Stereo-dynamical ion-pair formation in collisions of highly-charged ions with argon dimers

Multiple ionization process of a rare gas dimer BC collided with a slow highly charged ion A^q+ is investigated with the three-center Coulombic over-barrier model previously developed by the present authors. To reveal stereodynamical effects, we calculate asymmetric ion-pair formation cross sections σ(Q_B,Q_C) as a function of the orientation angle. We introduce a pair of atomic impact parameters b_B and b_C with which we distinguish the near and far sites. Furthermore, we distinguish the forward and backward emitted ions produced as a result of Coulomb explosion. Partial screening effects are also considered.