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The electronic structure and linear optical properties of luminescent material EuKNaTaO₅ are investigated by employing full-potential linear augmented plane wave method. Our results show highly localized Eu4f states which pinned in the energy range below the unoccupied Ta5d states and over the occupied O 2p states. The optical spectra are analyzed and interpreted in terms of the electronic structure. It is found that Eu ions absorb the major parts of the incident energy below 3.3 eV. This is in accordance with the experimental result that EuKNaTaO₅ phosphor is efficient under the excitation of 535 nm (2.3 eV) visible part of the spectrum. The linear optical properties are found to be anisotropic.

We have investigated how the wakes in the induced charge density and in the potential due to the passage of highly energetic partons through a thermal QCD medium get affected by the presence of strong magnetic field $(B)$. For that purpose, we wish to analyze first the dielectric responses of the medium both in presence and absence of strong magnetic field. Therefore, we have revisited the general form for the gluon self-energy tensor at finite temperature and finite magnetic field and then calculate the relevant structure functions at finite temperature and strong magnetic field limit (SMF: $\left|q_{f}B\right|\gg T^2$ as well as $\left|q_{f}B\right|\gg m_f^2$, $q_f(m_f)$ is the electric charge (mass) of $f$th flavor). We found that for slow moving partons, the real part of dielectric function is not affected by the magnetic field whereas for fast moving partons, for small $\left|k\right|$, it becomes very large and approaches towards its counterpart at $B=0$, for large $\left|k\right|$. On the other hand the imaginary part is decreased for both slow and fast moving partons, due to the fact that the imaginary contribution due to quark loop vanishes. With these ingredients, we found that the oscillation in the (scaled) induced charge density, due to the very fast partons becomes less pronounced in the presence of strong magnetic field whereas for smaller parton velocity, no significant change is observed. For the (scaled) wake potential along the motion of fast moving partons (which is of Lennard–Jones (LJ-)type), the depth of negative minimum in the backward region gets reduced drastically, resulting in the reduction of the amplitude of oscillation. On the other hand in the forward region, it remains as the screened Coulomb one, except the screening now becomes much stronger for higher parton velocity. Similarly for the wake potential transverse to the motion of partons in both forward and backward regions, the depth of LJ potential for fast moving partons gets decreased severely, but still retains the forward–backward symm etry. However, for lower parton velocity, the magnetic field does not affect it significantly.

The Wigner function is shown related to the quantum dielectric function derived from the quantum Vlasov equation (QVE), with and without a magnetic field, using a standard method in plasma physics with linear perturbations and a self-consistent mean field interaction via Poisson's equation. A finite-limit-of-integration Wigner function, with oscillatory behavior and negative values for free particles, is proposed. In the classical regimes, where the problem size is huge compared to the particle wavelength, these limits go to infinity, and for free particles, the Wigner function becomes a positive delta function as expected. For the harmonic oscillator potential, there is no distinction between finite and infinite limits of integration when these are larger than the eigenfunction localization length.

Within linear response theory, the dielectric and optical properties of a charged particle system are related to equilibrium correlation functions. In particular, the dynamical conductivity and the dynamical collision frequency are expressed in terms of the current-current or force-force correlation function, which can be evaluated analytically using perturbation expansions or numerically by MD simulations. Results are given for bulk material. Furthermore, finite systems such as laser excited clusters are considered. It is shown that the collision frequency is reduced in finite systems. The interaction with the laser field is discussed with respect to the current-current correlation function which changes with time due to the expansion of the laser-irradiated cluster.

The dielectric function of dense plasmas is treated within a many-particle linear response theory beyond the RPA. In the long-wavelength limit, the dynamical collision frequency can be introduced which is expressed in terms of momentum and force auto-correlation functions (ACF). Analytical expressions for the collision frequency are considered for bulk plasmas, and reasonable agreement with MD simulations is found. Different applications such as Thomson scattering, reflectivity, electric and magnetic transport properties are discussed. In particular, experimental results for the static conductivity of inert gas plasmas are now well described.

The transition from bulk properties to finite cluster properties is of particular interest. Within semiclassical MD simulations, single-time characteristics as well as two-time correlation functions are evaluated and analyzed. In particular, the Laplace transform of current and force ACFs show typical structures which are interpreted as collective modes of the microplasma. The damping rates of these modes are size dependent. They increase for the transition from small clusters to bulk plasmas.

The effect of doping with boron, carbon and nitrogen on crystal lattice parameters, electronic band structure and optical absorption of anatase has been studied by means of an ab initio density functional theory approach. The investigations included optimization of crystal structure based on the pseudo-potential plane-wave approach. The spin-polarized calculations of the band structure with the account of on-site Coulomb correlations (LSDA+U) employing the tight-binding linear muffin-tin orbitals method (TB-LMTO) have also been performed. The evaluations of optical absorption were based on the calculations of dielectric function with local field effects taken into account. We find that the crystal lattice relaxation around the doping atoms produces noticeable changes in the band structure, magnetic state and optical properties of the doped compounds. The most considerable effects are the collapse of magnetic moment on carbon atom and an essential reduction of the optical absorption in the region of the impurity band — impurity band transitions. Comparing optical absorption for different kinds of doping and taking into account the intensity distribution of the solar light we come to the conclusion than the doping with boron is the most promising kind of doping for photocatalytic applications of the doped anatase.

We calculate the dielectric function of a Weyl semimetal at arbitrary momentum q and frequency ω within the random-phase approximation. Taking the static limit, we calculated the Friedel oscillation and found that: (1) For a single Weyl point, the oscillation ~sin(2k_Fr)/r⁴ falls off faster by an 1/r factor than the one in traditional 3D systems ~cos(2k_Fr)/r³. This difference arises from the suppression of backward scattering in Weyl fermion systems; (2) For Weyl semimetal with two Weyl points, there are additional oscillations decaying as cos(Q ⋅ r)/r³ and cos(Q ± 2k_F) ⋅ r/r³, where Q is the momentum difference between the two Weyl points. We also calculated the plasmon dispersion and found features distinct from those of conventional 3D metals.

The structural, electronic, optical and vibrational properties of Ni₃C have been studied by density functional theory (DFT) framework with first-principles study. The obtained structural parameters are in good agreement with other works. The electronic study demonstrates metallic behavior of Ni₃C since it has no energy gap at Fermi level. The optical parameters such as real and imaginary dielectric functions, loss function, conductivity, reflection, refraction indexes and absorption coefficients are studied. The phonon investigations confirm that the Ni₃C bulk is dynamically stable and carbon has a major role in optical spectrum of the material at infrared region. Finally, the $T^3$ behavior of $C_v$ at low temperatures is obtained, as expected.

To determine the optical parameters of crude oil and seawater systems, we carried out spectral investigations using the ellipsometry method, which is a highly sensitive and accurate optical method for studying the surfaces and interfaces of various media. This method is based on studying the change in the polarization state of reflected light after its interaction with the surface of interfaces of these media. Crude oil and seawater from different regions of Caspian Sea were accessed by spectroscopic ellipsometry over the 200–1700 nm spectral range at room-temperature. Optical constants and dielectric function were obtained for massive samples of each substance, as well as for ultrathin layers of the oil spilled over the sea surface. Dielectric function, when completely determined in the frequency regions corresponding to electronic transitions and excitation of atomic or molecular vibrations in the object, is a unique dielectric fingerprint of this object. Oils with even miserable difference in type and concentration of biomarkers and heterocomponents will have different dielectric functions. The possibility to use dielectric function as a unique optical fingerprint for oil identification is figured out.

We have performed first-principle full-potential (linear) augmented plane wave plus local orbital calculations (FP-L/APW + l₀) with density functional theory (DFT) in local density approximation (LDA) and generalized gradient approximation (GGA), with the aim to determine and predict the electronic and optical properties of rocksalt BaO, BaS, BaSe, BaTe and BaPo compounds. First we present the main features of the electronic properties of these compounds, where the electronic band structure shows that the fundamental energy gap is indirect (Γ–X) for all compounds except for BaO which is direct (X–X). The different interband transitions have been determined from the imaginary part of the dielectric function. The real and imaginary parts of the dielectric function and the reflectivity are calculated. We have presented the assignment of the different optical transitions existing in these compounds from the imaginary part of the dielectric function spectra with respect to their correspondence in the electronic band. We have also calculated the pressure and volume dependence of the optical properties for these compounds.

First principles studies of structural, elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite under pressure are reported using the pseudopotential plane wave method within the local density approximation (LDA). The calculated equilibrium lattice is in good agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that tetragonal CaSiO₃ perovskite is a direct band gap material. In order to understand the optical properties of tetragonal CaSiO₃ perovskite, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 40 eV. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite, and it still awaits experimental confirmation.

In this paper, we present numerical calculations based on the full potential augmented plane wave (FP-LAPW) method within the local density approximation (LDA) to study the optical properties of the ternary alloy Al_xGa_1-xN. The shape of the dielectric function, the refractive index, and the absorption coefficient versus photon energy were presented. From the results, we deduce the possibility of this alloy to be used in the optoelectronic and photovololtaic area.

The dielectric function of a monolayer of molybdenum disulfide is investigated within the model of two-band metal using the random phase approximation (RPA). The large direct bandgap in a monolayer of MoS₂ leads to the appearance of the interband dipolar mode which couples to the intraband plasmon mode. This results in two hybridized modes. The renormalized dipolar mode is close to its bare value, while coupling suppresses the plasmon mode. The obtained modes are responsible for the appearance of dispersing peaks in the energy-loss function.

In this paper, we calculate a self-contained theoretical analysis of the dynamical response of the electron system in the fractional dimensional space within the random phase approximation. We find the static response function in several integer and non-integer dimensions. The plasma frequencies except in the quasi-one-dimensional system are damped into particle–hole excitation. In the long-wavelength limit the plasma frequency is finite at zero wave vector in three-dimensional system while these vanish at the same wave vector in the lower-dimensional systems.

First-principles calculations of ternary Sr₂ZnN₂ compound using density-functional theory (DFT) method within the generalized gradient approximation (GGA) has been performed. Based on the optimized structural parameter, the electronic properties and optical properties have been researched. The calculated lattice constants are in agreement with the experimental and theoretical results. The electronic structure have been investigated throughout the calculated band structure and density of states (DOS). It shows that this compound belongs to the semiconductors with a band gap of about 0.775eV. Furthermore, in order to clarify the optical transition of this material, the optical properties such as dielectric function, absorption coefficient, reflectivity, refractive index and energy-loss function at different pressures of 0, 10 and 20GPa in the energy range 0–20eV were performed and discussed. It shows that Sr₂ZnN₂ is a strong anisotropy material and the imaginary part of dielectric function shifts to higher energy region as the pressure increases. The square of calculated static refractive index is equal to static dielectric function, which corresponds to the theory formula. In conclusion, pressure is a effective method to change the electronic structure and optical properties.

In this paper, the structural, electronic and optical properties of LuPdBi and ScPdBi compounds are investigated using the density functional theory by WIEN2K package within the generalized gradient approximation, local density approximation, Engel–Vosco generalized gradient approximations and modified Becke–Johnson potential approaches. The topological phases and band orders of these compounds are studied. The effect of pressure on band inversion strength, electron density of states and the linear coefficient of the electronic specific heat of these compounds is investigated. Furthermore, the effect of pressure on real and imaginary parts of dielectric function, absorption and reflectivity coefficients of these compounds is studied.

In this study, we have developed and used the advanced high-precision numerical techniques to accurately calculate the optical properties and spin structure, and access the details of spin dynamics of the cobalt octaethylporphyrin (CoOEP) in the THz pulse magnetic field. The optical spectra of CoOEP are calculated using first-principles based on the GW approximation. The optical properties, including complex dielectric function, optical reflectivity, extinction coefficient, refractive index and absorption coefficient up to 10 eV, together with the calculated spin structure are considered. The spin structure of CoOEP is described by means of the density of spin transitions within the terahertz range. The study covers both terahertz and visible ranges. On the basis of the obtained optical theoretical spectra and the spin structure of CoOEP, it can be concluded that the applied complex approach provides a detailed and accurate description of the optical properties of cobalt octaethylporphyrin within the whole range of energies.

Using density functional theory and Boltzmann equations, this study calculates and compares the electronic, optical, thermoelectric, and thermodynamic properties of bulk and single-layer germanium carbide structures. It has been shown that germanium carbide in the bulk structure has an indirect energy band gap of 1.61eV. In a single layer structure, it is a metal. Thermodynamic properties including specific heat at constant volume have been investigated using the quasi-harmonic approximation (QHA) package in QE. According to the studies conducted on optical properties, this material shows good reflection in the visible region. In addition, this structure has high electrical conductivity and low thermal conductivity, which is essential for thermoelectric materials. Thermoelectric calculations using semi-classical Boltzmann transfer theory show that the performance of two-dimensional compounds with graphene gives good thermoelectric results. At 100K, the highest figure of merit (ZT) for GeC is 1.00. Our findings evaluate the GeC compound as a suitable thermoelectric material in the temperature gradient from 100 to 900K.

The electrical conductivity and volt–ampere characteristics (VAC) of the p-CuTlS₂ single crystal with specific resistance $\rho =40\mathrm{\Omega }\cdot \mathrm{\text{cm}}$ and irradiated by $\gamma$-quantum were studied in the range of 100–300K temperature and 10–10⁴V/cm. It was determined that the cause of the conduction disorder observed in the CuTlS₂ single crystal at low electric fields and high radiation doses is the formation of defect clusters dominated by cation vacancies. A sharp increase in current at high electric fields and temperatures occurs as a result of thermo-field ionization of the acceptor level with activation energy $\mathrm{\Delta }{E}_a=0.08$eV and the ionization voltage decreases with increasing radiation dose. Based on the determination of the parameters ($\lambda ,r_m,n_0,\epsilon$) that determine the mechanism of current flow, the dependence of the shape of the potential hole on the radiation dose was determined.

The optical properties of the various types of tapered silicon nanowires (SiNWs) have been investigated by the phase retrieving method of utilizing the experimental reflection spectra with the aid of the Kramers–Kronig (KK) relation. The effective refractive index (n) and the extinction coefficient (K) of each tapered SiNWs and combined silicon nanowires and microwires (CNMW) array samples can be obtained from concrete simulation by the KK relation. At the same time, we can also obtain the real part (ε′) and imaginary part (ε″) of the effective complex dielectric constant from the relation between the refractive index and the complex dielectric constant of samples. And the simulated results show that the relative material parameters (effective complex refractive index, effective complex dielectric function) can be modulated from a concrete material processing.