Partial Densities Of Electronic States Research Articles

Theoretical Study of the Magnetic Mechanism of a Pca21 C4N3 Monolayer and the Regulation of Its Magnetism by Gas Adsorption.

For metal-free low-dimensional ferromagnetic materials, a hopeful candidate for next-generation spintronic devices, investigating their magnetic mechanisms and exploring effective ways to regulate their magnetic properties are crucial for advancing their applications. Our work systematically investigated the origin of magnetism of a graphitic carbon nitride (Pca21 C4N3) monolayer based on the analysis on the partial electronic density of states. The magnetic moment of the Pca21 C4N3 originates from the spin-split of the 2pz orbit from special carbon (C) atoms and 2p orbit from N atoms around the Fermi energy, which was caused by the lone pair electrons in nitrogen (N) atoms. Notably, the magnetic moment of the Pca21 C4N3 monolayer could be effectively adjusted by adsorbing nitric oxide (NO) or oxygen (O2) gas molecules. The single magnetic electron from the adsorbed NO pairs with the unpaired electron in the N atom from the substrate, forming a Nsub-Nad bond, which reduces the system's magnetic moment from 4.00 μB to 2.99 μB. Moreover, the NO adsorption decreases the both spin-down and spin-up bandgaps, causing an increase in photoelectrical response efficiency. As for the case of O2 physisorption, it greatly enhances the magnetic moment of the Pca21 C4N3 monolayer from 4.00 μB to 6.00 μB through ferromagnetic coupling. This method of gas adsorption for tuning magnetic moments is reversible, simple, and cost-effective. Our findings reveal the magnetic mechanism of Pca21 C4N3 and its tunable magnetic performance realized by chemisorbing or physisorbing magnetic gas molecules, providing crucial theoretical foundations for the development and utilization of low-dimensional magnetic materials.

Exploration of the structure, electronic and optical properties of AB 2(PO3)5 polyphosphates: a first-principle approach

The density functional theory method was applied using the gradient PBE, incorporating the hybrid PBE0 functional along with dispersion corrections D3(BJ). These objectives were accomplished through the utilization of the CRYSTAL package, employing a localized atomic orbital basis. Calculations encompassing crystal properties, including electronic, structural, and linear/nonlinear opto-electronic characteristics, were conducted for monoclinic AB 2(PO3)5. Specifically, the polyphosphates investigated in this study are RbPb2(PO3)5, CsPb2(PO3)5, KBa2(PO3)5, and RbBa2(PO3)5. It was demonstrated that in monoclinic phosphates, phosphorus and oxygen atoms form infinite chains [PO4]∞ based on the· ⋯ O1-P-O1 ⋯ ·structure. Alkali metal and lead (barium) atoms are surrounded by oxygen atoms O2, forming polyhedra. Infrared absorption spectra calculations confirmed the presence of chain backbone structural units. Additionally, band structure and partial density of electronic states were determined. The nature of valence and unoccupied states was also investigated. In lead-doped compounds, lead atoms contribute to the formation of upper-valence and lower-unoccupied states. Conversely, in barium-doped compounds, the upper valence states are primarily formed by O2 p-states, while the lower unoccupied states are formed by phosphorus. Also, the coefficients of second harmonic generation and birefringence were calculated, assessing the potential use of phosphates as nonlinear optical materials.

Ce3Bi4Ni3 – A large hybridization-gap variant of Ce3Bi4Pt3

The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce3Bi4Ni3. It is an isoelectronic analog of the prototypical Kondo insulator Ce3Bi4Pt3 and of the recently discovered Weyl-Kondo semimetal Ce3Bi4Pd3. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce3Bi4Ni3 relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65–70 meV, about eight times larger than that in Ce3Bi4Pt3 and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce3Bi4Pd3. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce3Bi4Ni3−Ce3Bi4Pd3−Ce3Bi4Pt3, but instead with increasing partial electronic density of states of the d orbitals at the Fermi energy. This work opens the possibility to investigate the conditions under which topological states develop in this series of strongly correlated 3-4-3 materials. Published by the American Physical Society 2024

First-principles study of structural, electronic and magnetic properties of diluted magnetic semiconductor and superlattices based‏ on Cr-doped ZnS and ZnSe compounds in wurtzite-type crystal

We performed first-principle calculations to investigate the structural, electronic, and magnetic properties of ZnS and ZnSe binary compounds, Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices in the wurtzite structure using the full potential linear muffin–tin orbital (FP-LMTO) method. Features such as lattice constant, modulus of compressibility and its first derivative, spin-polarized band structures, total and local or partial electronic densities of states and magnetic properties were calculated. The electronic structure shows that Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices are half-metallic ferromagnetic with 100% complete spin polarization. The total magnetic moments calculated show the same integer value of 4 µB, which confirms the ferromagnetic half-metallic behavior of these compounds. We found that the ferromagnetic state is stabilized by the p-d exchange associated with the double-exchange mechanism. Zn0.5Cr0.5S and Zn0.5Cr0.5Se DMS alloys and (ZnS)2/Zn0.5Cr0.5Se and (ZnSe)2/Zn0.5Cr0.5S superlattices are shown to be promising new candidates for applications in the fields of spintronics.

Electronic structure and composition of tin oxide thin epitaxial and magnetron layers according to synchrotron XANES studies

The materials of the tin-oxygen system and thin-film structures based on them are modern and actual for the creation of a wide range of electronic devices, for example, resistive gas sensors of high sensitivity and short response time with low energy consumption and high manufacturability. An important direction in the study of such materials and structures is the control of properties with variations in technological formation regimes. Information on the composition, local atomic and electronic structure of thin layers of the tin-oxygen system with varying approaches to their production is in demand. The work is devoted to the study of the electronic structure of thin layers of tin oxides obtained by modern methods of molecular beam epitaxy and magnetron sputtering. A study of the local partial density of electronic states in the conduction band by X-ray absorption near edge structure spectroscopy of tin and oxygen has been carried out. The data were obtained using high-intensity synchrotron radiation, which allows varying the monochromatized radiation quantum energy without loss in intensity, that is necessary to obtain high-resolution X-ray spectral data. It is shown that the composition, local atomic surrounding, electronic spectrum and their features depend on the technology of formation and storage conditions of the studied structures. Synchrotron X-ray spectroscopy data show the presence of intermediate oxides of the tin-oxygen system in the studied materials after prolonged storage in laboratory conditions. The data obtained indicate the possibility of controlled variation in the composition, local atomic surrounding and electronic spectrum of thin-film structures of tin oxides of small thickness. The results of the work can be used in the formation and subsequent modification of thin and ultrathin layers of tin oxides by magnetron sputtering and molecular beam epitaxy, as well as in their further application as active layers of microelectronics devices

First-principles simulations of magnetic properties of Co- and Ni-doped ZnSe

We purposed to analyze the theoretical ab initio study of ferromagnetism and to estimate Curie temperature of Co2+ and Ni2+ 3d transition metal (TM) ions doped Zn1-x TM x Se compounds for 12.5 % and 6.25 % concentrations of impurity TM(Co, Ni) atoms. The calculations are carried out using the norm-conserving Fritz-Haber-Institute ionic pseudopotentials based on density functional theory within the local spin density approximation and Hubbard U (U(Znd)=4.5 eV; U(Sep)=3.8 eV) corrections. The analysis of the total and partial electron density of states shows the half-metallic ferromagnetic behavior with a half-metallic bandgap. The theoretically obtained total magnetic moments of TM(Co, Ni) doped Zn1-x TM x Se systems are equal to 3 μB and 4 μB, correspondingly.

Effect of codoping of rare earth elements and Cr on multiferroic, optical and photocatalytic properties of BiFeO3

In the present work, first principle calculations have been performed to study the combined effect of A (Bi) and B (Fe) site doping on the structural, multiferroic, optical and photocatalytic properties of BiFeO3 (BFO). Rare earth elements (La, Ce, Gd, Nd, Er and Eu) are doped at the A-site while Cr is doped at the B-site in perovskite BFO. A variation in total magnetic moments and spontaneous polarization of the doped systems is observed that are governed by the introduction of the rare earth elements. A maximum polarization of 110μC/cm2 is obtained for (Gd,Cr) doped BFO and the maximum magnetization of 5.1μB/cell is obtained for (Nd,Cr) doped BFO. From the study of partial electronic density of states it has been observed that amongst all the dopants incorporated as rare earth elements, the (Er,Cr)BFO system exhibits the minimum bandgap of 1.94 eV and thus shifts the absorption edge deep into the visible region which has been confirmed through the optical spectra. The band-edge alignment of the pure and codoped systems has revealed that (Er,Cr)BFO exhibits the maximum potential to be a promising photocatalyst with improved efficiency as compared to pristine BFO.

Electronic structure of germanium dioxide with rutile structure according to ab initio computer simulation data

The article focuses on the electronic structure of the tetragonal crystalline modification of germanium dioxide. The electronic structure was theoretically studied by means of the full-potential linearized augmented plane wave method using the Wien2k software. Total and partial densities of electronic states were calculated. The spectra of the X-ray absorption near edge structure were simulated for various absorption edges of germanium and oxygen atoms. The Z+1 approximation method was used to calculate Ge K-, Ge L3- and O K absorption edges for the tetragonal modification of GeO2. The result obtained for the Ge K absorption edge is in good agreement with the experimental data. The Ge L3 spectrum was calculated for the first time, and the result is of predictive nature. In order to obtain a better agreement with the experimental calculations of the oxygen K absorption edge, besides the Z+1 approximation method, we also used the core hole method, including the simulation of a partial core hole. The study demonstrated that the use of a core hole with an electron charge of 0.7 results in a better agreement between the calculations and the experiment

Atomic and electronic structures of an Ag-containing 4A zeolite

Atomic structure of an Ag-containing 4A zeolite with the Ag/Al atomic ratio of about 10% was investigated by a pair distribution function (pdf) analysis. Valence- and conduction-band O 2p partial electronic structures of this insulating material were respectively measured by soft X-ray emission and absorption spectroscopies using an O 1s-2p resonance technique. Moreover, a density functional theory (DFT) hybridized by 25% of Hartree–Fock exchange was applied to determine the atomic structures and electronic states. Although the box size of the DFT calculation was small due to the limited computational power, the present DFT results excellently reproduce the pdf data as well as O 2p partial electron density of states (DOS). The electronic charge distributions in this zeolite with an antibacterial function obtained by the present DFT calculation revealed half-filled charges on the Ag atoms, which may act as a formation of deactivating the bacteria.

The Electronic Structure and Optical Spectroscopy of ErNi2Mnx Compounds

The electronic structure and optical properties of nonstoichiometric ErNi2Mnx compounds (with х = 0, 0.5, 1) have been studied. Spin-polarization calculations of the total and partial densities of electron states have been performed in terms of DFT + U method with a correction for strong electronic correlations in the 4f shell of Er in the approximation of ErNi2 – xMnx solid-solution. The peculiarities of transformations of the densities of electron states Have been determined depending on the manganese content. The optical properties of these compounds have been studied over a wide wave length range. The calculated interband optical conductivity spectra have been compared with the dependences obtained experimentally. The origin of the quantum absorption of light is discussed. The plasma and relaxation frequencies of current carriers have been determined.

Электронная структура и рентгеноспектральные характеристики полупроводниковой и металлической фаз дисилицида железа

Within the framework of the full-potential method of augmented plane waves with local orbitals, the electronic structure and X-ray spectral characteristics of the semiconductor and metal phases of iron disilicide were calculated. The total and partial densities of electronic states, the band structure, and X-ray absorption spectra of the iron K-edge were calculated. The results are compared with the known experimental data. An explanation is given of the change in the X-ray absorption near edge structure during the transition from the semiconductor phase to the metallic one.

Electronic structure and X-ray spectral characteristics of the semiconductor and metal phases of iron disilicide

Within the framework of the full-potential method of augmented plane waves with local orbitals, the electronic structure and X-ray spectral characteristics of the semiconductor and metal phases of iron disilicide were calculated. The total and partial densities of electronic states, the band structure, and X-ray absorption spectra of the iron K-edge were calculated. The results are compared with the known experimental data. An explanation is given of the change in the X-ray absorption near edge structure during the transition from the semiconductor phase to the metallic one. Keywords: iron disilicide, electronic structure, APW+lo, method, XANES, K-edge.

Intercalation of Sr in AA stacked bilayer graphene : DFT study of the electronic structure and optical properties

We report the structure, electronic band structures, and total and partial electron density of states of strontium intercalation in the A A bilayer of graphene (Sr-intercalated AA stacked BG) from first-principles calculations. Our results show that the Sr intercalation influences the electronic properties. Indeed, we observed the contribution of the Sr atom to the band gap formation. The p and d orbitals of the Sr atom have a remarkable contribution to the formation of the DOS of the Sr-intercalated AA stacked BG. The Dirac point where the gap is non-zero in the AA stacked BG is located at about 1 . 38 e V below the Fermi level. Thus, the electron density is maximal around the C atoms, which leads to an efficient transfer of electric charges from the Sr atom to the C atoms. In addition, we have exploited the complex dielectric function to calculate the absorption coefficient, refractive index, and extinction index. The static refractive index increases in vertical polarization and diverges in parallel mode, confirming the pure metallic behavior of the Sr-intercalated AA stacked BG material. Moreover, the value of the absorption coefficient in the visible region increases in the vertical mode while it decreases in the parallel direction. These results indicate that AA stacked BG intercalated by Sr has relevant properties for optoelectronic and ultrafast devices.

New insights into the interaction between monomers from acrylamide-based polymeric flocculants and montmorillonite: A DFT study

Montmorillonite (MMT) is the main clay mineral in mine wastewater and also the most difficult fine particles to treat. In order to explore how common acrylamide-based organic polymeric flocculants interact with montmorillonite surfaces on micro scale, three kinds of active monomers of acrylamide-based organic polymeric flocculants were selected, and the microcosmic mechanism between the three active monomers and MMT (001) and (010) surfaces was analyzed by density functional theory (DFT). The simulation results of adsorption energy, charge analysis and partial electronic density of states show that the three studied monomers can be adsorbed on the (001) and (010) surfaces and 2-acryloyloxyethyltrimethyl-ammonium chloride (DAC) adsorbed more strongly than 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), which in turn adsorbed more strongly than acrylamide (AM). The adsorption on (001) surface is more favorable because the three active monomers can be stably adsorbed at both the easy and hard hydration sites on (001) surface, while only stably adsorbed at the hard hydration sites on (010) surface. After adsorption, the stronger the delocalization of the PDOS on the same surface, the shorter the hydrogen bond length and the larger the population value. Electrostatic interaction dominates the adsorption process on the Na-MMT (001) surface, whereas hydrogen bonding dominates the adsorption mechanism on the Na-MMT (010) surface. This research provides theoretical guidance for the design and synthesis of novel selective flocculants.

Bandgap and electronic structure of CaSiN2: Experiment and theory

AbstractWe interrogate the electronic properties of the nitridosilicate CaSiN2 as determined using soft X‐ray absorption and emission spectroscopy, which probe directly the partial electronic density of states. We compare our measurements to full potential, all electron density functional theory (DFT) calculations. Good agreement between experiment and theory is obtained, and the electronic bandgap of CaSiN2 is determined to be 3.95 ± 0.3 eV, in contrast with our predicted value of 4.78 eV that was calculated using the modified Becke–Johnson exchange‐correlation functional with the DFT framework.

Low-dimensional Magnetism in Compounds with Different Dimensions of Magnetic Interaction

The results of a comparison of the exchange interaction mechanisms in low dimensional magnetic systems are presented. It has been shown that ZnO crystal may be used as a semiconductor non-magnetic matrix for the formation of quasi-one-dimensional and quasi-zero-dimensional magnetic systems by introducing impurity atoms of Cr, Mn, Fe, Co and Ni. Structural parameters, electronic and magnetic properties were calculated at the atomic level in the framework of quantum mechanical simulation. The exchange interaction integrals were calculated at the microscopic level using the Heisenberg model. The exchange interaction mechanisms were determined on the obtained dependences of the exchange interaction integral on the structural and electronic properties, as well as on the features of the low-dimensional magnetic systems partial density of electronic states. The results of studying the exchange interaction mechanisms in two-dimensional magnetic systems formed in materials of the MAX3 (M= Cr, Fe, A = Ge, Si, X= S, Se, Te) group are summarized. The established mechanisms made it possible to compare the conditions for the formation of a ferromagnetic order in systems with different dimensions of magnetic interaction. The ferromagnetic order in all the structures under study is formed due to the indirect superexchange interaction between orbitals of different symmetry. Strategies aimed at enhancing the superexchange interactions between orbitals of different symmetry or attenuating the contributions of the exchange interaction between orbitals of the same symmetry contribute to the formation of stable hightemperature ferromagnetism.

Preparation, electronic structure and optical properties of Na2GeSe3 crystals

From the first principles, in the framework of the density functional theory in LDA and LDA+U approximations, the band structure, total and partial densities of electronic states, spatial distribution of the electron charge density, also the optical functions: dielectric constant, refractive and absorption indices, reflection and absorption coefficients of Na2GeSе3 crystal have been calculated. According to the calculation results, Na2GeSе3 is a direct-gap crystal with the top of valence band and the bottom of conduction band at the point Г of Brillouin zone. The calculated band gap is Egd = 1.7 eV LDA and Egd = 2.6 eV in the LDA+U approximations. Based on the data of total and partial densities of electronic states, contributions of atomic orbitals to the crystalline ones have been determined. Also, the data of chemical bond formation in the crystals under discussion have been obtained.

Growth of a novel K0.4Rb0.6Pb2Cl5 crystal and theoretical and experimental studies of its electronic and optical properties

We report on successful growth by Bridgman method of an optical quality K0.4Rb0.6Pb2Cl5 crystal and determination of its crystal structure and electronic and optical properties. In particular, the present results indicate that the K0.4Rb0.6Pb2Cl5 crystal crystallizes in monoclinic space group P21/c, with the unit-cell parameters as follows: a = 8.9484(2) Å, b = 7.9802(2) Å, c = 12.5359 Å, and β = 90.1220(10)°. For the K0.4Rb0.6Pb2Cl5 crystal, we use X-ray photoelectron spectroscopy (XPS) to measure binding energies of the core-level electrons for constituting atoms and to reveal the energy distribution of the valence electronic states. Our XPS measurements indicate very low hygroscopicity of the K0.4Rb0.6Pb2Cl5 crystal surface and partial alteration from Pb2+ ions to Pb0 when using bombardment with 3 kV Ar + ions. To find peculiarities of filling the valence band and the conduction band of the K0.4Rb0.6Pb2Cl5 crystal by partial densities of electronic states associated with the composing atoms, we apply different approaches for exchange-correlation potential using model K0.5Rb0.5Pb2Cl5 solid solution. We have found that the finest agreement of the experimental and theoretical data is derived when in the calculating procedure we use Tran-Blaha modified Becke-Johnson (TB-mBJ) potential involving spin-orbit coupling and the Hubbard parameter U (TB-mBJ + U + SOC approach). The present theoretical TB-mBJ + U + SOC results predict that K0.5Rb0.5Pb2Cl5 is a non-direct material with energy band gap of 4.167 eV. The optical properties of K0.5Rb0.5Pb2Cl5 are elucidated theoretically in detail based on first-principles calculations within the TB-mBJ + U + SOC model.

Детерминизм локального атомного упорядочения в монослоях золота в формировании их электронной структуры

The total and partial densities of electronic states of gold monolayer structures of different symmetry are calculated by the quantum mechanical calculations methods in the DFT approximation. It is shown that the first coordination sphere is determinant in the formation of the fine structure and the extent of the valence bands of the monolayer gold structures under study. The peaks splitting of the TDOS curve, which leads to its finer structure, is influenced not only by the lengths of interatomic bonds but also by the mutual arrangement of atoms. The influence of long-range interactions on the electronic structure of gold monolayers has been established. For example, for the (110) plane, a change in the atomic ordering in the third coordination sphere as a result of the introduction of a vacancy leads to noticeable changes in the TDOS curve, which indicates either a significant role of the atoms of the third coordination sphere or a significant redistribution of the interaction of d-orbitals of different symmetries of close neighbours. A correlation between the packing density, as well as the number of neighbours in the first coordination sphere, and the width of the energy band of gold monolayers has been established.

АТОМНАЯ И ЭЛЕКТРОННАЯ СТРУКТУРЫ ХИРАЛЬНЫХ ЗОЛОТЫХ НАНОТРУБОК

The article presents the results of a study of the atomic and electronic structure of gold nanotubes that do not have mirror symmetry. The elementary cells of nanotubes (4, 3) and (5, 3) are constructed and their properties are modeled in the framework of the density functional theory using periodic boundary conditions. Different behavior of two types of interatomic distances was established during the “twisting” of the triangular lattice of the nanotube wall. The bonds in first one turned out to be noticeably shorter than in nanotubes with mirror symmetry. The features of the electronic structure and partial densities of electronic states, in general, turned out to be regardless of the presence of mirror symmetry.