JOURNAL OF RESEARCH ON MANY BODY SYSTEMS
Year:2019 | Volume:9 | Issue:3 (22)|Papers Count:18

The electronic structure of various TiO2 structures were calculated using PBE and HSE06 functionals. The calculated band gaps in HSE06 level for rutile and anatase phases was 3. 4 and 3. 58 eV, respectively, which are in agreement with the experimental values of 3 and 3. 2 eV. The calculated bulk moduli for the mentioned phases were 226 and 205 Gpa. The differences between these values and the reported experimental values are 7% and 14%, respectively. A comparison between the two mentioned functionals shows that the overall form of band structures is independent of the functional. Particularly, the top of the valence band and the bottom of the conduction band are the same in PBE and HSE06. Therefore, both functionals give the same result for the type (direct or indirect) of band-gap. The distance between conduction and valence bands, and consequently the band-gap, is the main difference in calculating the band-structure using these two functionals. The band-gap difference calculated by these functionals is almost 1. 6 eV for all the structures investigated in this study. Therefore, one can calculate the band-gap of TiO2 with PBE and sum the result by 1. 6 eV instead of calculating the band gap in expensive HSE06 level, which is close to the experimental value.

In this paper, we used magnetic nanoparticles to improve the degradation of diazinon. For this purpose, iron oxide nanoparticles (Fe3O4) were synthesized by modified hydrothermal method. Subsequently, we used the ultrasonic method and put a shell of SiO2nanoparticles on it. The obtained nanoparticles were then characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), Vibrational Sampler Magnetic Meter (VSM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM). The x-ray diffraction pattern showed the inverse spinel structure of nanoparticles. The residual curve of the pure iron oxide sample showed 74 saturation magnetization. For the core-shell, the saturation magnetization was 42 , all confirming the paramagnetic properties of nanoparticles. These nanoparticles exhibit superparamagnetic properties. The results of the transient electron microscope indicate the formation of this shell on iron oxide nanoparticles. Finally, these nanoparticles were used to degrade diazinon in aqueous solutions with different concentrations. Cetyltrimethylammonium bromide (CTAB) was used as an organic cationic surfactant to improve the degradation of diazinon.

In this paper, we consider a spin chain with cluster interaction which is under the transverse magnetic field. We also study its dynamical behavior as the magnetic field changes suddenly. This system has an exact solution by means of Jordan-Wigner transformations. We show that if the magnetic field changes in such a way that its initial and finial value are in two different equilibrium phases, then the rate function of return probability diverges periodically in time. In case this divergence is in time, it is called dynamical phase transition. If the quench has been done within the same phase, dynamical phase transition will not occur. Furthermore, we have shown that Fisher zero lines cross the imaginary axes when the dynamical phase transition occurs.

Borophene is a monolayer of boron atoms with many allotropes. The electrical and mechanical properties of  12 borophene are investigated using density functional theory.  12 borophene has an orthorhombic lattice with five boron atoms in a unit cell. We calculated the critical strain and ultimate stress of the sheet. The calculated critical strain is 0. 18% in the x-direction with the ultimate stress of 18. 87 N/m while the critical strain is 10% and 12% for uniaxial strain along y and the biaxial strain, respectively. Young’ s modulus of the sheet is 180 N/m in the x-direction and 203 N/m along the y one. Structural defects reduce the mechanical ability of the sheet, and this reduction is strongly dependent on the position of the removed atoms and their density.

Interesting electronic and catalytic properties of two-dimensional MoS2 few-layers have recently attracted the attention of researchers. In this paper, the synthesis of MoS2 nanoflakes standing on the SiO2/Si substrate in the process of rapid sulfidation by chemical vapor deposition has been reported. Material characterization was performed using Raman spectroscopy, XRD and FESEM. The XRD results indicate the dominant phase of 2H-MoS2 and the distance between the two leading peaks of E 1 2g and A1g in the Raman dispersion confirms the thickness of 6 to 10 atomic layers. According to the experimental data, the growth mechanism was introduced based on the nucleation and the growth of two-dimensional islands. In the next stage, it was based on the coalescence of these two-dimensional islands, and in the final stage, it was based on the growth of standing nanoflakes. These structures, which have active sites on the edges, have many potential and promising applications in fine transistors, gas sensors and catalytic reactions.

By employing the quantum chaos theory, a metal-insulator transition was investigated in a single-walled graphene nanotube affected by vacancies based on the tight-binding Hamiltonian. The obtained results indicate that applying an electric field along the axis of the defected graphene nanotube caused metal to insulator transition. Using the spectral and multifractal analyses, the threshold value of the electric field was determined. The results show that in the absence of the electric field, the defected nanotube shows a metallic behavior with the Wigner distribution. By increasing the value of the electrical field, the level spacing distribution changes from Wigner (delocalized) to Poisson (localized) distribution. such that for the threshold value of the electrical field, Poisson level spacing sets in.

In this work, nickel thin films were first deposited on silicon and quartz substrates by the electron beam evaporation technique at the same deposition conditions. Then the prepared films were annealed at different temperatures of 400-700 ° C in an electrical furnace. The effect of annealing temperature on the structural, morphological and optical properties of samples were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV-Vis spectrophotometry. XRD results revealed the formation of crystalline nickel phases in the annealing temperature of 400 ° C and by increasing the annealing temperature from 500 ° C to 700 ° C, the crystalline nickel oxide phases were observed. The AFM and SEM images showed that the annealing temperature effectively influenced the morphology and surface roughness of films and the grain sizes were increased by enhancing the annealing temperature. Also the optical band gap values of nickel oxide films deposited on quartz substrates were calculated from transmittance data.

In this study, waveguide properties of graphene nanoribbon on hBN and a substrate were investigated. Precisely, the plasmonic mode properties including the real part of refractive index, the propagation length, figure-of-merit (FoM) on frequency, the Fermi energy of graphene, and the substrate in the mid-IR spectrum range were inspected. The simulated results show that graphene waveguide is intensively sensitive to the frequency, Fermi energy and structural geometry in the mid-IR range. Also, the propagation length for a Fermi energy of 0. 3 (0. 9) eV in the frequency range of 1375 cm-1 to 1600 cm-1 reaches from 0. 1 (0. 4) to 0. 38 (4. 15) µ m, where it shows a 3-(10)-fold enhancement.

Using the particle-in-cell method, the behavior of the dusty plasma under plasma fusion conditions of Tokomak's wall and the effect of the magnetic field on the process of dusty plasma particles were simulated and examined. The electric field is self-consistently solved from Poisson's equation. Electron-neutral elastic scattering, excitation, and ionization processes are modeled using Monte-Carlo collision method. The effect of the difference in the initial density of the plasma and the different magnetic field was simulated, and their results were compared together. The time to reach the saturation state and the amount of the saturated charge were obtained in the process of charging dust particles. It was observed that increasing the magnetic field does not necessarily mean an increase in the charge of dust particles or a decrease in the time to reach the saturation state. Finding the limit of this field, which certainly depends on the physical properties of the plasma, can be useful in some issues, for example, in plasma fusion conditions and labs. Some of the limitations of current theoretical models in the interaction of dust particles and plasma and the gap in the current empirical and theoretical approaches are described in the study of dust in fusion devices.

Topological phases can be induced in single and bilayer graphene in the presence of appropriate spin-orbit coupling and external potentials. We survey the characteristics of the different metallic 1D zero-line channels at bulk-vacuum edges and at interfaces between regions with different bulk topological orders in single and bilayer graphene. We use a tight-binding Hamiltonian for ribbon geometries to study the characteristics of the 1D zero-line channels appearing at the interfaces between regions of different topological phases. Depending on the resulting states, the number of 1D metallic channels at interface and edge differ so that these can be thought as a characterization of the states.

In this paper, the electronic structure of a two-dimensional quantum ring under the influence of external electric and magnetic fields are studied in the presence of Rashba and Dresselhaus spin-orbit interactions. To do this, at first, the effective Hamiltonian of the system is demonstrated in the presence of applied electric and magnetic fields by considering the spin-orbit coupling. Afterwards, the Schrodinger equation is solved using the matrix diagonalization approach. Then, we investigate the effects of external fields and the size of the ring on the eigenvalues of the system. Our results indicate that spin-orbit interactions, external fields and the ring size have a great influence on the electronic structure of the system.

In this study, the structural, electrical and optical properties of fullerene C20 with different numbers of Be atoms attached on its surface are investigated. The results showed that the stability of nano-clusters increased by adding the number of Be atoms. By increasing the number of Be atoms around C20, the HOMO-LUMO gap was generally decreased, but the highest decrease was observed in Eg in the Be4@C20-trans and Be6@C20 structures which were 0. 69 and 0. 49, respectively. Also, properties such as ionization potential (I), electron affinity (A), chemical potential (μ ), total hardness (η ), total softness (γ ), electrophilicity (ω ), and electronegativity (χ ) were calculated as electrical properties. The polarizability (α ) and the first hyperpolarizability (β 0), which are related to linear and nonlinear optical properties (NLO), were calculated. A significant increase in the first hyperpolarizability (β 0>1000000) was observed by doping 6 atoms of Be on the C20 surface. The results of this study may be used to design and construct nanomaterials with adjustable electrical properties.

A main class of machine learning approaches aims at predicting a label or value of some quantity from a set of input data (e. g., recognizing a face from the pixels of a digital image). As an example of the application of such techniques in computational condensed matter physics, we demonstrate, in this study, an accurate prediction of the atomic contributions into a given physical quantity from the arrangement of neighboring atoms. We introduce a descriptor that quantifies the environment of each atom and is filled by the eigenvalues of an approximate Coulomb matrix. The descriptor is invariant under rotation or translation of the molecule and the permutation of the atomic indices. It captures fine structural deformations including the change of the four-body, dihedral angles. Employing this atomic descriptor, we exemplify a promising case where the charges on different atomic species in the molecule are predicted by machine learning to within one tenth of the elementary charge.

A hybrid positron source based on the channeling radiation (CR) of relativistic electrons on different planes and axes of Si, C, Ge, and W crystals is investigated. We have calculated CR spectra from different planes and axes of Si, C, Ge and the W crystal using the Doyle– Turner approximation for the continuum potentials of crystallographic planes and axes. The dependence of CR on the incidence angle of electrons is also investigated. CR is then impinging on an amorphous tungsten target producing positrons by e +--e pair creation. The simulations are made with our developed Mathematica codes, which calculate the photon CR in the crystal target and GEANT4 code which calculates the materialization of photons into e +--e pairs in the amorphous W target. The results of this work are in good agreement with other results.

In the present paper, three body dHeμ and pHeμ systems have been considered using a trial wave function in the variational method. The governing interaction for these ions is the Coulomb interaction and is considered in the hyper sphere coordinate system. In this method, firstly, the wave function is divided into hyper-angle and hyper-radius and then the Schrodinger equation has been solved. The energy eigen values have been calculated for the ions and finally the present results have been compared with available data. Using the given wave function and the energy we can obtain other structure parameters. The resulting energy levels in this study for pHeμ and dHeμ molecules are − 73. 021 and − 76. 728, respectively. The relative error percents in this study, compared with other studies, are less than %1. 135 and %1 for pHeμ and dHeμ molecules, respectively.

In this paper, a Hamiltonian model, which includes the interaction of two two-level atoms with a codirectional Kerr nonlinear coupler via the Raman non-degenerate two-photon transition, is introduced. The atomic interaction is assumed to be in the dipole-dipole form, and the total system is also in thermal equilibrium with the environment. The total excitation number operator, as the constant of the motion of the system, provides a decomposition of the Hilbert space of system into direct sums of invariant subspaces. As a result, the representation of the Hamiltonian becomes a block-diagonal matrix. By diagonalizing each of the blocks, we obtain eigenvalues and the corresponding eigenstates of the Hamiltonian. Then we obtain the thermal state of the system in the whole Hilbert space and within its excitation subspaces. We quantify the thermal entanglement between the atoms in the Hilbert space of the system and within its excitation subspaces using the measure of the concurrence. Finally, the effect of temperature and system parameters on the degree of thermal entanglement is investigated. The results show that in the subspaces with an odd excitation number, the atomic thermal entanglement is thermally robust and remains constant.

Quantum teleportation is the transmission and reconstruction of the state of a quantum system over arbitrary distances. Since the possibility of transferring quantum information is one of the foundations of newly-emerging fields of science such as quantum communication and quantum computation, in this article quantum teleportation of a qubit will be investigated via an entangled channel. To this aim, we will use two-mode entangled coherent channels generated by beam splitter and Kerr medium. It will be shown that the amount of entanglement and fidelity of quantum teleportation depend on the intensity of the coherent state such that when the intensity of coherent state increases sharply (p=0), the entanglement and the average fidelity reach a maximum, Fmax=1. On the other hand, considering the fact that real physical systems are always affected by their surroundings, investigation of the effects of environment, as a source of quantum dissipation on entanglement and fidelity, will be very important. In this article, the effects of amplitude damping on average fidelity of quantum teleportation will be analyzed. The results show that the average fidelity is decreased by increasing amplitude damping. Moreover, the loss of fidelity in maximally entangled channels is more than that of non-maximally entangled channels.

In the present study, the zeroth-and first-order radiative correction of the Casimir energy for massive and massless scalar fields, confined with mixed boundary conditions (DirichletNeumann) between two parallel plates in  4 theory, were computed. Two issues in performing calculations in this work are essential: first, to renormalize the bare parameters of the problem, a systematic method was used, which allows all influences from the boundary conditions to be imported in all elements of the renormalization program. This idea yields our counterterms appearing in the renormalization program to be position-dependent. Using the box subtraction scheme as a regularization technique is the other noteworthy point in the calculation. In this scheme, by subtracting the vacuum energies of two similar configurations from each other, regularizing divergent expressions and their removal process were significantly facilitated. All the obtained answers for the Casimir energy with the mixed boundary condition were consistent with well-known physical grounds. We also compared the Casimir energy for the massive scalar field confined with four types of boundary conditions (Dirichlet, Neumann, a mix of them and Periodic) in 3+1 dimensions with each other, and the sign and magnitude of their values were discussed.