Density Of States Plots Research Articles

Electronic properties of a quantum ring perturbed with a quantum well in the presence of perpendicular magnetic flux

Here, we study the effects of the number of sites, quantum ring radius and potential well depth on the energy levels, persistent current, magnetic susceptibility and density of states (DOS) of a quantum ring with a quantum well within its circumstance in a magnetic flux perpendicular to its plane. We show that, for small radius quantum ring systems, there are periodic local gaps along the magnetic flux axis in the DOS plots and along the axis ‘energy’. For large radius quantum ring systems, a uniform gap along the energy axis exists and along the phi axis nothing changes. In quantum rings with a quantum well in their circumstance, by using the large confining potential, we can create uniform gaps in the Energy–phi plane. The energy eigenvalues, persistent current and magnetic susceptibility decrease by increasing the confining potential. A quantum ring even with a very small confining potential in its circumstance can sensibly decrease the persistent current and magnetic susceptibility, although it may do not change the energy eigenvalues and DOS maximum considerably. Thus, by using the abovementioned parameters, we are able to tune the DOS, persistent current, magnetic susceptibility and energy levels, desirably.

Ab-initio study of electronic, magnetic and thermoelectric behaviors of LiV2O4 and LiCr2O4 using modified Becke-Johson (mBJ) potential

Owing to the large energy storage capacity and higher working voltage, the spinel oxides LiV2O4 and LiCr2O4, have remained under intense research attention for utilization as electrode materials in lithium-ion batteries. In this study, we explore the half-metallic nature and thermoelectric response in both LiV2O4 and LiCr2O4 spinel oxides using ab-initio density functional theory (DFT) based computations. The ground-state energies of these compounds have been studied at the optimized structural parameters in the ferromagnetic phase. In order to obtain a correct picture of the electronic structure and magnetic properties, the modified Becke-Johnson (mBJ) potential is applied to compute the electronic structures. The half-metallic behavior is confirmed by the spin-polarized electronic band structures and density of state plots. The magnetic nature is elucidated by computing the John-Teller energy, direct and indirect exchange and crystal field splitting energies. Our computations indicate strong hybridization decreasing the V/Cr site magnetic moments and increasing magnetic momenta at the nonmagnetic atomic sites. We also present the computed parameters significant for expressing the thermoelectric response, which are electrical conductivity, thermal conductivity, See-beck coefficient and power factor. The computed properties are of immense interest owing to the potential spintronics and Li-ion battery applications of the studied spinel materials.

Decomposition Mechanisms of Anti-wear Lubricant Additive Tricresyl Phosphate on Iron Surfaces Using DFT and Atomistic Thermodynamic Studies

Tricresyl Phosphate (TCP) is widely used as an anti-wear additive for lubrication and hydraulic fluid technology in aerospace propulsion systems. However, there is no clear description of the chemistry involved in the conversion of TCP to an anti-wear film on metal surfaces. Different reaction mechanisms leading to different product formation have been described in the literature, but no attempts have been made to explain the interfacial chemistry using first principles theoretical methods. In this study, we employed density functional theory with atomistic thermodynamic modeling to study the decomposition mechanisms of TCP on an iron (110) surface. We considered three broad reaction schemes, namely TCP as phosphoric acid reservoir, thermal decomposition of TCP, and TCP decomposition by hydrolysis. Different reaction paths were considered for the three reaction schemes, and the resulting decomposition products were characterized by the change in reaction energy, density of state plots, Bader charge analysis, and work functions. We observed that all three reaction schemes had at least one pathway with decreasing reaction energy, indicating they are likely to proceed in the proposed reaction direction. In the presence of hydrogen, TCP decomposition proceeded through the phosphoric acid reservoir mechanism with the anti-wear film comprised of a phosphate group, an m-tolyl group and 1-methyl-2,5-cyclohexadiene. In the presence of moisture, TCP decomposed through hydrolysis leading to a film comprised of a phosphate group and 3-methyl-2,5-cyclohexadienol. However, in the absence of hydrogen and moisture, film formation proceeded through thermal decomposition, and the resulting film was comprised of a methylphenoxy group, a P=O group, and 3-methyl-3,5-cyclohexadienone. Several of the products formed in the calculations, such as a phosphate group, methylphenoxy group, P=O groups, and di-cresyl phosphate, have been observed experimentally in previous research, but we also observed new products, including 3-methyl-2,5-cyclohexadienol and 1-methyl-2,5-cyclohexadiene.

Ab-initio studies of the structural, electronic, optical and magnetic properties of DyMg intermetallic compound

Abstract Structural, electronic, optical and magnetic properties of DyMg intermetallic compound are calculated by using the full potential linearized augmented plane wave (FP-LAPW) method employing density functional theory (DFT). The obtained optimized equilibrium lattice constant in stable structure of DyMg (B2 phase) with spin polarized calculations is 7.107 Bohr and that without spin polarized calculations is 7.115 Bohr. The electronic band structure and density of states plots show metallic character of DyMg. The energy-dependent components of dielectric function, refractive index, extinction coefficient, absorption spectra, optical conductivity, energy loss spectra and reflectivity are reported in the energy range 0–20 eV. In DyMg maximum absorption is observed in the range 4–11 eV. The highest optical conductivity peak is observed near 0.78 eV (1589.5409 nm) and maximum energy loss occurs at 11.90 eV which corresponds to ~2.8 Hz in ultraviolet region. The obtained total magnetic moment shows that its value decreases with the increase in lattice parameter.

First-principles investigation on the mechanical and electronic properties of novel Pb1−xCexY alloys (Y = S, Se, and Te): an ab initio study

The first-principles full-potential linearized augmented plane-waves with local orbitals approximation within the density functional theory is used to treat in detail the structural, elastic, and electronic properties of new Pb1−xCexY (Y = S, Se, and Te) alloys at different concentrations (x = 0.25, 0.50, and 0.75). The generalized gradient approximation of calculations show that the ground stable state of Pb1−xCexY alloys is in rock-salt structure, where the equilibrium structural parameters such as, lattice constant, bulk modulus, and its first pressure derivative are performed and compared to the previous theoretical and experimental data. The elastic study is considered to determine the elastic moduli C11, C12, and C44 of the cubic crystal. Through the obtained results of the elastic moduli, the derivative mechanical moduli including Young’s modulus, shear modulus, Poisson’s ratio, Kleinman parameter, and anisotropy factor are calculated in the fact to demonstrate the mechanical stability of these alloys. The nature of the electronic structure of these studied alloys is characterized with the help of the band structure and the density of states plots.

Electronic properties of B and Al doped graphane: A hybrid density functional study

Using a hybrid density functional theory approach parametrized by Heyd, Scuseria and Ernzerhof (HSE06 hybrid functional), we study the energetics, structural and electronic properties of a graphane monolayer substitutionally doped with the B (BCH) and Al (AlCH) atoms. The BCH defect can be integrated within a graphane monolayer at a relative low formation energy, without major structural distortions and symmetry breaking. The AlCH defect relaxes outward of the monolayer and breaks the symmetry. The density of states plots indicate that BCH doped graphane monolayer is a wide band gap semiconductor, whereas the AlCH defect introduces the spin dependent mid gap states at the vicinity of the Fermi level, revealing a metallic character with the pronounced magnetic features. We further examine the response of the Al dependent spin states on the multiple charge states doping. We find that the defect formation energy, structural and electronic properties can be altered via charge state modulation. The +1 charge doping opens an energy band gap of 1.75eV. This value corresponds to the wavelength in the visible spectrum, suggesting an ideal material for solar cell absorbers. Our study fine tunes the graphane band gap through the foreign atom doping as well as via defect charge state modulation.

Theoretical Investigation of Cubic BaVO3 and LaVO3 Perovskites via Tran–Blaha-Modified Becke–Johnson Exchange Potential Approach

The full potential linearized augmented plane wave method of density functional theory has been used to investigate the structural, electronic, magnetic and thermoelectric properties of cubic perovskites BaVO3 and LaVO3. The ferromagnetic ground state has been found to be stable by comparing the total energies of non-spin-polarized and spin-polarized calculations performed for optimized unit cells. For both compounds, the bond length and tolerance factor are also measured. From the band structures and density of states plots, it is found that both compounds are half-metallic. We found that the presence of V at the octahedral site of these perovskites develops exchange splitting through p-d hybridization, which results in a stable ferromagnetic state. The observed exchange splitting is further clarified from the magnetic moment, charge and spin of the anion and cations. Finally, we also presented the calculated thermoelectric properties of these materials, which show that half-metallic BaVO3 and LaVO3 materials are potential contenders for thermoelectric applications.

GFETSIM: Graphene Field-Effect Transistor Simulator of Interface Charge Density

The discovery of graphene by Andre Geim and Konstantin Novoselov in 2004 contributed significantly to complementary metal-oxide-semiconductor (CMOS) technology, especially for electronic devices. Due to its outstanding properties, graphene has been used in many applications such as field-effect transistors (FETs), touch-sensitive screens, liquid-crystal displays, light-emitting diodes, dye-sensitised solar cells, and organic solar cells. Consequently, interface charge density in graphene field-effect transistors has become an important area of research in order to more accurately determine electronic characteristics such as capacitance-voltage (C-V). In this research, we developed a comprehensive simulation tool based on graphene FET called graphene field-effect transistor simulator (GFETSIM) of interface charge density, which functions as a graphical user interface (GUI) using MATLAB. This simulation represents the on-going development of a carbon-based device simulator begun in 2014 at Universiti Teknologi Malaysia (UTM). An automated selfconsistent approach is utilised to extract and compute the interface charge density. It is coded in MATLAB and the program was developed into an interactive MATLAB GUI simulation tool. The interface for GFETSIM is generated using the graphical user interface development environment (GUIDE) in MATLAB. This simulator allows users to import external C-V data into the GUI and carry out analysis based on the density of states plots. In addition, key parameter values can be varied to assess the outcome and changes in interface trapped density. In addition, a reset button is embedded into the simulator.

Structural, electronic and magnetic properties of metal thiophosphate InPS4

The non-centrosymmetric crystal, InPS4, has been investigated by means of density functional theory (DFT). In this paper we have calculated the structural parameters, electronic band structures, density of states plot and magnetic properties using full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation has been solved employing the generalised gradient approximation due to Perdew-Burke-Ernzerhof. The calculations are performed both without spin as well as spin polarized. The results show that InPS4 is an indirect band gap semiconductor with (N-Г) energy gap of 2.32eV (without spin) and 1.86eV in spin up and down channels.The obtained lattice parameters and energy gap agree well with the experimental results. Our reported magnetic moment results show that the property of InPS4is nonmagnetic.

Molecular Oxygen Adsorbed on Gallium Doped Graphene: A First-Principles Study

The adsorption of molecular oxygen on gallium doped graphene sheet is investigated using first-principles density functional theory calculations. The adsorption energy of O2 on gallium doped graphene is calculated after determining the energetically favourable adsorption configuration. The change in the electronic properties of gallium doped graphene after O2 adsorption is also determined to understand the nature their interactions. The results show that gallium doped graphene has large adsorption energy and small binding distance, which correspond to chemical adsorption. The calculated band structure and density of states plots of gallium doped graphene before and after adsorption show dramatic changes in the electronic properties due to the strong interactions of gallium doped graphene with adsorbed O2 molecule. These results indicate that gallium doped graphene is highly reactive to molecular oxygen and hence not a suitable choice for harmful gas detection in the presence of O2.

Tailored Au and Pt Containing Multi-metallic Nanocomposites for a Promising Fuel Cell Reaction

The development of an efficient syntheses method to produce multimetallic nanocomposites with an appropriate structure is required to study the structure–composition–property relationship of the synthesized nanocomposites and to investigate, evaluate their possible technological applications. In this work, a fine hetero-structured Au and Pt containing multi-metallic nanocomposites (Au/Pt/Ag and Au/Pd/Pt colloidal nanocomposites) were synthesized through a microwave irradiation method with the use of trisodium citrate as a reducing agent and it has been coated on the glassy carbon electrode. It is characterized by high-resolution transmission electron microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopic techniques to elucidate structure, surface morphology, bulk-composition and metallic state of the resulting Au/Pt/Ag and Au/Pd/Pt colloidal nanocomposites respectively. The colloidal nanocomposites were also characterized by zeta potential and dynamic light scattering studies. The electrochemical techniques (cyclic voltammetry and chronoamperometry) have been employed to investigate the electrochemical parameters related to the electro-oxidation of methanol which in turn will be useful for conventional fuel cell applications. In addition to that, the density functional theoretical optimized minimum-energy structures of Pt n (n = 3–6) were studied as they are forming shell and thus involved in catalysis. Electronic density of state plots of the optimized Pt n and Pd n clusters using B3LYP/Lanl2DZ level of theory was made. The multi-metallic nanocomposites of these metals are proposed as a promising new class of catalyst for the electro-oxidation reaction of methanol particularly in fuel-cell applications. The formation of hetero-structure is discussed as the desirable condition to obtain a better electrocatalytic activity. It is also found that, the electrocatalytic activity and stability of the resultant Au/Pt/Ag colloidal nanocomposites modified glassy carbon electrode is much better catalyst towards methanol electrooxidation in acid medium.

K1.33Mn8O16 as an electrocatalyst and a cathode

Density functional theory (DFT) calculations are carried out to investigate the electronic, magnetic and thermoelectric properties of bulk and nanosheet K1.33Mn8O16 materials. The catalytic activity and cathodic performance of bulk and nanosheet structures are examined using the Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potential. Electronic structure calculations reveal an anti-ferromagnetic ground state, with a TB-mMBJ band gap in bulk K1.33Mn8O16 that is in agreement with experimental results. Density of state plots indicate a partial reduction of Mn4+ ions to Mn3+, without any obvious sign of Jahn-Teller distortion. Moreover, use of the O p-band center as a descriptor of catalytic activity suggests that the nanosheet has enhanced catalytic activity compared to the bulk structure. Thermoelectric parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity are also calculated, and it is found that the Seebeck coefficients decrease with increasing temperature. High Seebeck coefficients for both spin-up and spin-down states are found in the nanosheet relative to their value in the bulk K1.33Mn8O16 structure, whereas the electrical and thermal conductivity are reduced relative to the bulk. In addition, figures of merit values are calculated as a function of the chemical potential and it is found that the nanosheet has a figure of merit of ~1 at room temperature, compared to 0.5 for the bulk material. All results suggest that K1.33Mn8O16 nanosheets can be used both as a material in waste heat recovery and as an electrocatalyst in fuel cells and batteries.

Systematic study of room-temperature ferromagnetism and the optical response of Zn1−xTMxS/Se (TM = Mn, Fe, Co, Ni) ferromagnets: first-principle approach

The structural, magnetic and optical characteristics of Zn1−xTMxS/Se (TM = Mn, Fe, Co, Ni and x = 6.25%) have been investigated through the full-potential linearized augmented plane wave method within the framework of density functional theory. The optimized structures have been used to calculate the ferromagnetic and the antiferromagnetic ground-state energies. The stability of the ferromagnetic phase has been confirmed from the formation and the cohesive energies. The Heisenberg model is used to elucidate the Curie temperature (Tc) of these alloys. From the band structures and density of states plots, it has been observed that TM-doped ZnS/Se alloys appear to be semiconductors and exhibit ferromagnetism. In addition, the observed ferromagnetism has also been explained in terms of direct exchange energy Δx(d), exchange splitting energy Δx(pd), crystal-field energy (Ecrys), exchange constants (N0α and N0β) and magnetic moments that shows potential spintronic applications. The optical behaviors of these alloys have been explained in terms of real and imaginary parts of the dielectric constant ε(ω), refractive index n(ω), extinction coefficient K(ω), reflectivity R(ω) and absorption coefficient σ(ω), in the energy range 0–25 eV. The calculated static limits of the band gaps and real part of the dielectric constants satisfy the Penn model. The critical limits of the imaginary part of the dielectric constants and absorption coefficients indicate that these alloys can be operated in the visible and the ultraviolet region of the electromagnetic spectrum; therefore, make them important for optoelectronic applications.

Facet-dependent electrical conductivity properties of Cu2O crystals.

It is interesting to examine facet-dependent electrical properties of single Cu2O crystals, because such study greatly advances our understanding of various facet effects exhibited by semiconductors. We show a Cu2O octahedron is highly conductive, a cube is moderately conductive, and a rhombic dodecahedron is nonconductive. The conductivity differences are ascribed to the presence of a thin surface layer having different degrees of band bending. When electrical connection was made on two different facets of a rhombicuboctahedron, a diode-like response was obtained, demonstrating the potential of using single polyhedral nanocrystals as functional electronic components. Density of state (DOS) plots for three layers of Cu2O (111), (100), and (110) planes show respective metallic, semimetal, and semiconducting band structures. By examining DOS plots for varying number of planes, the surface layer thicknesses responsible for the facet-dependent electrical properties of Cu2O crystals have been determined to be below 1.5 nm for these facets.

First principles study on energetic, structural, and electronic properties of defective g-C3N4-zz3 nanotubes

The energetic, electronic and structural properties of defective g- C 3 N 4-zz3 nanotubes are considered based on spin-polarized density-functional theory calculations. Nine basic system types with vacancy defects are characterized by their stabilization energies and band gaps. It is found that the nitrogen atom denoted as N 3 is the most favorable atom for a vacancy defect. In all cases, local bond reconstruction occurs in the presence of vacancy defects. The role of C / N bond rotations on the above properties has been also investigated. The results show that N 1– C 3 bond rotation is the most favorable rotational defect. In addition, the electronic properties of the semiconducting g- C 3 N 4-zz3 nanotube with defects have been studied using band structure and density of states plots.

Investigation of thermoelectric properties of half-metallic Co2MnGe by using first principles calculations

By combining the electronic structures obtained from first principles calculations with Boltzmann transport theory we have investigated the electronic, magnetic and transport properties of the Co2MnGe Heusler compound. The density of state plots, dispersion curves and the total energy of paramagnetic and ferromagnetic (FM) phases clearly show the half-metallic FM ground state for the compound, with an indirect band gap of about 400 meV in the minority spin channel. It has an integer value of the magnetic moment equal to 5 μB. In the FM phase a very large value (∼ 550 µV K−1) of the Seebeck coefficient (S) is obtained for down-spin electrons due to the existence of an almost flat conduction band along X in the Γ direction. The two-current model has been used to find the total S and the obtained value is about 10 µV K−1. The calculated values of the Seebeck coefficient, resistivity and electronic thermal conductivity show nice agreement with the experimental results.

Impact of co-adsorbed oxygen on crotonaldehyde adsorption over gold nanoclusters: a computational study

Crotonaldehyde (2-butenal) adsorption over gold sub-nanometer particles, and the influence of co-adsorbed oxygen, has been systematically investigated by computational methods. Using density functional theory, the adsorption energetics of crotonaldehyde on bare and oxidised gold clusters (Au13, d = 0.8 nm) were determined as a function of oxygen coverage and coordination geometry. At low oxygen coverage, sites are available for which crotonaldehyde adsorption is enhanced relative to bare Au clusters by 10 kJ mol(-1). At higher oxygen coverage, crotonaldehyde is forced to adsorb in close proximity to oxygen weakening adsorption by up to 60 kJ mol(-1) relative to bare Au. Bonding geometries, density of states plots and Bader analysis, are used to elucidate crotonaldehyde bonding to gold nanoparticles in terms of partial electron transfer from Au to crotonaldehyde, and note that donation to gold from crotonaldehyde also becomes significant following metal oxidation. At high oxygen coverage we find that all molecular adsorption sites have a neighbouring, destabilising, oxygen adatom so that despite enhanced donation, crotonaldehyde adsorption is always weakened by steric interactions. For a larger cluster (Au38, d = 1.1 nm) crotonaldehyde adsorption is destabilized in this way even at a low oxygen coverage. These findings provide a quantitative framework to underpin the experimentally observed influence of oxygen on the selective oxidation of crotyl alcohol to crotonaldehyde over gold and gold-palladium alloys.

Role of Defects on structural and electronic properties of zigzag C3N nanotubes: A first-principle study

The energetic, electronic, and structural properties of zigzag C3N nanotubes with defects have been systematically investigated through the spin-polarized density-functional theory calculations. The four basic system types with Stone–Wales defects are characterized in terms of the defect stabilization energy and the band gaps. The most desirable bond rotation is related to a circumferential N–C bond. The role of vacancy defects on the above properties has been also investigated. Our results show that carbon vacancy is more favorable than nitrogen vacancy. Moreover, the electronic properties of the semiconducting C3N nanotubes with defects have been studied using band structures and density of states plots.

Hybrid density functional based study on the band structure of trioctahedral mica and its dependence on the variation of Fe2+ content

A hybrid density functional based study of a phyllosilicate (PS) is presented here for the first time. Using all-electron electronic structure calculations with the B3LYP hybrid functional, we have investigated the electronic and structural properties of a series of trioctahedral 1M-polytype K-bearing micas starting from phlogopite (the Mg-end member), ending with the annite (the Fe-end member), and passing through the biotite (a solid solution of the end members). Electronic band gap is calculated for all the compositions and nature of the electronic transition is discussed with the aid of band structure and density of states plots. An excellent agreement with the available experimental data has been observed. An insulator to semiconductor transition is explained on the basis of orbital hybridization. A further comparison is made using the pure GGA functional. For the completeness of the study, the dielectric properties of phlogopite are calculated using the coupled perturbed Kohn–Sham scheme, as implemented within the CRYSTAL09 code.

First-principles investigation on the electronic and magnetic properties of cubic Be0.75Mn0.25X (X=S, Se, Te)

The structural, electronic and magnetic parameters of Be0.75Mn0.25X (X = S, Se, Te) are investigated using first-principles calculations. The thermodynamic stability of these Mn-doped semiconductors can be confirmed by the negative energetic quantities of formation energy and cohesive energy, and the stability decrease from Be0.75Mn0.25S to Be0.75Mn0.25Te with the magnitude of energetic quantities decrease as the same order. Calculated from the band structures, Be0.75Mn0.25X have smaller band gaps (1.49 eV, 1.36 eV, 0.78 eV for X = S, Se, Te, respectively) than BeX. The density of states and valence electron distribution plots indicate that the atomic bonding of Be0.75Mn0.25X is mainly contributed from the interactions between Mn-d and X-p. And the electronic interaction weakens from Be0.75Mn0.25S to Be0.75Mn0.25Te. The local magnetic moment of Mn, the exchange splitting energies, and exchange constants can be obtained from the spin-polarized electronic structures and density of states plots, the splitting energy Δx(d) is positive while Δx(pd) is negative, the exchange constants N0α and N0β are negative. And all of them increase along with X atom radius increasing, which implies the effective potential for down-spin is more attractive than that for up-spin, and it decreases along with the X atom changing from S to Te. N0α and N0β suggest that the interactions of Be(2s)–Mn(3d) states and X(p)–Mn(3d) states are all attractive, and the interactions of s–d and p–d weakens with the same sequence.