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In this work, all-d metal Heusler alloys Ni–Mn–Cr were predicted by first principles. Their structure, magnetism, tetragonal distortion and electronic properties were studied. The cubic groud state structures of Ni 2 MnCr and NiMnCr 2 are XA type, and that of NiMn 2 Cr is L2 1 type. All of them have magnetism. The change of their lattice constants is closely related to the covalent radius of atoms. Ni 2 MnCr has a stable tetragonal phase and may undergo martensitic transition. NiMn 2 Cr has a lower energy tetragonal phase, but is dynamically unstable. The equilibrium volumes of the two compounds expand through tetragonal distortion. NiMnCr 2 does not have a lower energy tetragonal phase. In the tetragonal distortion, the atomic magnetic moments are influnced by the interatomic distance and the magnetic moments of neighboring atoms. The origin of the tetragonal distortion and magnetic properties was discussed in terms of the electronic density of states. • Ni 2 MnCr and NiMnCr 2 have an XA-type structure, NiMn 2 Cr has an L2 1 structure, and all of them exhibit magnetism. • Ni 2 MnCr has a stable tetragonal phase and may undergo martensitic transition. • The atomic magnetic moments are influenced by the interatomic distance and the magnetic moments of neighboring atoms. • The Jahn-Teller effect triggers the tetragonal distortion. [ABSTRACT FROM AUTHOR]

This study investigated the energy band structure (BS), electronic state density, and optical properties of monolayer molybdenum disulfide (ML-MoS 2) with undoped, sulfur vacancy (V S), bromine (Br), and iodine (I) doped MoS 2 systems using the first-principle approach based on density functional theory (DFT). Our results show that compared to undoped MoS 2 system, Br, and I doped MoS 2 systems induced lattice distortions. In addition, and the bandgap widths was reduced in V S , Br, and I doped systems, thereby effectively suppressing the compounding of electron–hole pairs. Moreover, the recombination rate of electron–hole pairs was reduced, which in turn increased the mobility of electrons transferred from the valence band (VB) to the conduction band (CB). Moreover, the V S and Br doped systems exhibited superior optical properties compared to undoped MoS 2 system. Notably, the V S system exhibited the best optical properties, thereby demonstrating the strongest polarization capability. Our findings pave the way for realizing electronic devices and photocatalytic materials on MoS 2 nanostructures. [Display omitted] • Lattice distortion of monolayer MoS 2 by the introduction of V S , Br, and I doping elements. • The introduction of V S and Br doping element enhances the electron mobility of monolayer MoS 2. • The introduction of V S and Br doping element enhances the utilization of monolayer MoS 2 for infrared and visible light. [ABSTRACT FROM AUTHOR]

The interaction of kaolinite and water has been extensively investigated by scholars in geomechanics and high-pressure physics fields. As well known, the effects of pressure on the adsorption capacity of clay mineral cannot be ignored. In the present paper, the adsorption behaviors of water molecules with different coverage (0 ≤ Θ ≤ 1 ML) on the kaolinite (001) surface under the pressure range of 0–10 GPa were examined using density functional theory (DFT). The atomic structure of kaolinite has undergone phase transitions under high pressure. The transition pressures of kaolinite occurred at 4.93 GPa (kaolinite-I → kaolinite-II) and 8.23 GPa (kaolinite-II → kaolinite-III), respectively. The results revealed that the hollow sites of kaolinite-Ⅰ, Ⅱ, and Ⅲ (001) surface were the most stable adsorption sites for water molecules at different coverages. The order of adsorption capability for three phases kaolinite was kaolinite-Ⅰ > kaolinite-Ⅱ > kaolinite-Ⅲ. In the pressure range of 0∼10 GPa, the adsorption energies of water molecules on the three phases of kaolinite (001) surfaces increased with increasing coverage (0 ≤ Θ < 1/2 ML) and then decreased with increasing coverage (1/2 < Θ ≤ 1 ML). For three phases kaolinite, the adsorption energies decreased with increasing pressure at 1/16 and 1/4 ML, while the changes of adsorption energies at other coverages with increasing pressure didn't exhibit obvious consistent regularity. Further exploration was performed on the structure and electronic properties change within the adsorption process by studying the lattice relaxation, and electronic density of states (DOS) of the adsorption system of (001) surface and water molecules. • The order of adsorption capability for three phases kaolinite was kaolinite-Ⅰ > kaolinite-Ⅱ > kaolinite-Ⅲ. • The adsorption energies of water molecules on the three phases of kaolinite (001) surfaces increased with increasing coverage (0 ≤ Θ < 1/2 ML) and then decreased with increasing coverage (1/2 < Θ ≤ 1 ML). • For three phases kaolinite, the adsorption energies decreased with increasing pressure at 1/16 and 1/4 ML. [ABSTRACT FROM AUTHOR]

Abstract The stability and band alignments of ZnO on (112) LaAlO 3 substrates are studied by first-principles calculations. We have created the ZnO/LaAlO 3 heterostructure by consideration of the initial adsorption of the first ZnO layers on (112) LaAlO 3 surfaces. The atomic charges, electronic density of states, and band alignment are systematically analyzed for the optimized ZnO/LaAlO 3 heterojunction. The ZnO/LaAlO-terminated LaAlO 3 heterostructure is a potential candidate for the design of ZnO-based metal oxide semiconductor devices because the band offsets are larger than 1 eV and the interface does not produce any gap states. Highlights • Band alignment for the ZnO/LaAlO 3 heterostructure. • The initial adsorption structure of the first ZnO layers on (112) LaAlO 3 surfaces. • The ZnO/LaAlO interface is suitable for metal insulator semiconductor devices. [ABSTRACT FROM AUTHOR]

Computational calculations of total energy based on density functional theory were used to investigate the structural, electronic, and magnetic properties of the DyB 2 compounds in the hexagonal structure. The calculations were carried out by means of the full-potential linearized augmented plane wave (FP-LAPW) method, employing the computational Wien2k package. The local density approximation (LDA) and the generalized gradient approximation (GGA) were used for the electron-electron interactions. Additionally, we used the functional hybrid PBE0 for a better description the electronic and magnetic properties, because the DyB 2 compound is a strongly-correlated system. We found that the calculated lattice constant agrees well with the values reported theoretically and experimentally. The density of states (DOS) calculation shows that the compound exhibits a metallic behavior and has magnetic properties, with a total magnetic moment of 5.47 μ 0 /cell determined mainly by the 4 f states of the rare earth elements. The functional PBE0 shows a strong localization of the Dy-4 f orbitals. [ABSTRACT FROM AUTHOR]

Heavy metal (HM) pollution is of great concern currently because it has been recognized as a potential threat to air, water,and soil. Adsorption is one of the most effective strategies for removing heavy metals. Montmorillonite as the adsorbent with a low cost and high thermal stability has received much attention. The adsorption of heavy metal Copper [Cu(II)] and Plumbum [Pb(II)] atoms on Na-montmorillonite hydroxylated (010) edge surface was analyzed using the generalized gradient approximation and density functional theory in the supercell technique. The coverage dependence of the adsorption structure and energetics was systematically investigated for a wide range of coverage from 0 to 1.0 monolayer (ML). Among all the possible adsorption sites, the most stable adsorption site for Cu(II) atom was a three-fold hollow site while the most favorable adsorption site for Pb(II) atom was a three-fold hollow site and followed by a two-fold bridge site. The adsorption energy increased with increasing coverage of Pb(II) atoms, indicating higher stability of surface adsorption and a tendency for the formation of adsorbate island clusters with increasing coverage. However, the adsorption energy of Cu(II) atoms decreased with increasing coverage. In the coverage range of 0 < Θ ≤ 0.5 ML the recovery capacity of the Na-montmorillonite for the heavy metal atoms was in the order of Cu(II)>Pb(II), while the recovery capacity of the Na-montmorillonite in the coverage range of 0.5 < Θ ≤ 1 ML was in the order of Pb(II)>Cu(II). The other aspects of the Cu(II) and Pb(II)/Na-montmorillonite (010) systems, including adsorption geometry, differential charge distribution, and electronic density of states were also studied and discussed in detail. • We investigated the adsorption of Cu(II) and Pb(II) on montmorillonite (010) surface. • The most stable adsorbed site for Cu(II) and Pb(II) is three-fold hollow site. • The adsorption energy of Pb(II) atoms increased with increasing coverage. • The adsorption energy of Cu(II) atoms decreased with increasing coverage. [ABSTRACT FROM AUTHOR]

First-principles calculations, were carried out to study the structural stability of the cubic [ (F m 3 ‾ m) , (F 4 ‾ 3 m) ] and tetragonal [ (I 4 / m m m) , (I 4 ‾ m 2) ] phases, of R u 2 V Z (S i ; G e) full Heusler compounds; where Energy of formation, elastic, Mechanical, phonon and thermodynamic properties and electronic density of states were determined. Through our results, all ferromagnetic phases exhibit a total magnetic moment of 1 μ B for both R u 2 V S i and R u 2 V G e compounds, except the tetragonal (I 4 ‾ m 2) phase that manifest a zero ( 0 μ B) total magnetic moment.Further, the antiferromagnetic state of the cubic phase F m 3 ‾ m R u 2 V Z (S i ; G e) was found energetically more favorable than the ferromagnetic one.The analysis of the calculated elastic and dynamic properties, revealed that only the regular cubic phase (F m 3 ‾ m) of the R u 2 V S i and the regular tetragonal phase (I 4 / m m m) of the R u 2 V G e are the most stable among the considered phases. The calculated electronic density of states for the ferromagnetic stable phases, confirm the existence of a half-metal character with high spin polarization (P n) of: ∼ 91 % and ∼ 100 % for the R u 2 V S i and R u 2 V G e respectively. • In This article applied the Full full-potential linearized augmented-plane-wave method (FP-LAPW) to the determination of the structural, dynamic mechanical and electronic properties of the two full Heusler compounds R u 2 V S i and R u 2 V G e. • The antiferromagnetic state for the cubic (F m 3 ‾ m) R u 2 V Z (S i ; G e) compounds was found more favorable than the ferromagnetic one. • The analysis of the calculated elastic and dynamic properties, show that only the regular cubic phase (F m 3 ‾ m)) of the R u 2 V S i and the regular tetragonal phase (I 4 / m m m) of the R u 2 V G e are the most stable among the considered phases. • The electronic density of states for the ferromagnetic stable phases, confirm the half-metal character with high spin polarization for the R u 2 V S i and R u 2 V G e respectively. [ABSTRACT FROM AUTHOR]

In this work, we have studied the influences of electron-phonon (e-ph) coupling and chemical potential on the boron nitride graphene-like sheet. In particular, by starting the Green's function technique and Holstein model, the electronic density of states (DOS), electronic heat capacity (EHC) and magnetic susceptibility (MS) of this system have been investigated in the context of self-consistent second order perturbation theory which has been implemented to find the electronic self-energy. Our findings show that the band gap size decreases (increases) with e-ph coupling (chemical potential) parameters. The Schottky anomaly (crossover) decreases in EHC (MS) as soon as e-ph coupling increases. Also, the corresponding temperature with Schottky anomaly is considerably affected by e-ph coupling. [ABSTRACT FROM AUTHOR]

The structural, thermodynamic, mechanical and electronic properties of cubic Al 2 Sm intermetallic compound are investigated by the first-principles method on the basis of density functional theory. In light of the strong on-site Coulomb repulsion between the highly localized 4f electrons of Sm atoms, the local spin density approximation approach paired with additional Hubbard terms is employed to achieve appropriate results. Moreover, to examine the reliability of this study, the experimental value of lattice parameter is procured from the analysis of the TEM image and diffraction pattern of Al 2 Sm phase in the AZ31 alloy to verify the authenticity of the results originated from the computational method. The value of cohesive energy reveals Al 2 Sm to be a stable in absolute zero Kelvin. According to the stability criteria, the subject of this work is mechanically stable. Afterward, elastic moduli are deduced by performing Voigt-Reuss-Hill approximation. Furthermore, elastic anisotropy and anisotropy of sound velocity are discussed. Finally, the calculation of electronic density of states is implemented to explore the underlying mechanism of structural stability. [ABSTRACT FROM AUTHOR]

Using scanning tunneling spectroscopy and theoretical simulations we have studied the effects of nitrogen gas exposure on the electronic density of states of Bi 2 Se 3 , a well-studied topological insulator. In carefully controlled measurements, Bi 2 Se 3 crystals were initially cleaved in a helium gas environment and then exposed to a 22 SCFH flow of ultra-high purity N 2 gas. We observe a resulting change in the spectral curves, with the exposure effect saturating after approximately 50 min, ultimately bringing the Dirac point about 50 meV closer to the Fermi level. These results are compared to density functional theory calculations, which support a picture of N 2 molecules physisorbing near Se vacancies. Furthermore, ab initio molecular dynamics simulations aided by a Blue Moon ensemble method reveal the dissociative adsorption of N 2 molecules which then bind strongly to Se vacancies at the surface. In this scenario, the binding of the N atom to a Se vacancy site removes the surface defect state created by the vacancy and changes the position of the Fermi energy with respect to the Dirac point. • Scanning tunneling microscopy experiments show evidence of N 2 exposure effect on Bi 2 Se 3. • A shift in the tunneling conductance spectra is observed in real time. • Density functional theory calculations provide supporting evidence. • Blue moon ensemble method provides a molecular dynamics model. [ABSTRACT FROM AUTHOR]

We have presented a theoretical study for the coexistence of superconductivity (SC) and Jahn–Teller (JT) effect with applied magnetic field on iron based high- T c superconductors in s -wave symmetry. The analytic expressions for the temperature dependence of the SC and JT order parameters are derived by Zubarev's technique of double time single particle Green's function method and solved self-consistently. It is observed that in the interplay region, both the gap parameters exhibit very strong dependence of their gap values. The effect of external magnetic field on the gap parameters and the electronic density of states (DOS) is studied. [ABSTRACT FROM AUTHOR]

We report thermoelectric properties of Cu 2 O powder through interface modification. Seebeck coefficient (SC) of Cu 2 O–Au composite powder was measured to be 900–1500 μV/K in the temperature range of 300–420 K, and power factor was ∼1.95 μW/m⋅K2 at 420 K, in contrast to raw Cu 2 O powder (0.86 μW/m⋅K2). The improved Seebeck coefficient and power factor relate very likely to the band structure modification by Au atoms, energy filtering and remote doping. Optic measurement and band structure calculated using density functional theory confirmed the band gap of Cu 2 O–Au composite powder (1.78eV) is slightly narrower than the raw Cu 2 O powder (1.85eV) and higher electronic density of states (DOS) in the conductance band of Cu 2 O–Au composite powder. Powder form thermoelectric devices (P-TE) easily prepared by pressing in a die without sintering might offer an alternative paradigm for mass fabrication with low cost. The high Seebeck coefficient and power factor of P-TE could find applications as power generator, temperature/touch sensors, transient thermoelectric coolers, etc. • We measured Seebeck coefficient of Cu 2 O powder as high as 1500 μV/K. • A very facile fabrication process was used (No ball milling, no sintering):Cu 2 O powder deposited of Au by sputtering. • Band structure modification by Au atoms, energy filtering and remote doping for improved thermoelectric performance. [ABSTRACT FROM AUTHOR]

Based on density functional theory (DFT), the structural, martensitic transition, band structure, density of states, elastic, magnetic, and thermoelectric properties of L2 1 and XA ordering of Co 2 FeGe compound were investigated. The calculated total energy shows that the most stable phase of these compounds is the L2 1 type with ferromagnetic state using GGA + U approach. In addition, the possible martensitic transition is occurring for L2 1 phase which has minimum energy localized at c/a = 1.02. The electronic density of states (DOS) and band structure of Co 2 FeGe exhibit a ferromagnetic metallic for both L2 1 and XA phases. From the calculated elastic constants show that the studied phases are elastically anisotropic and satisfies Born′s criteria for mechanical stability. Moreover, through the quasi-harmonic Debye model applied in the Gibbs codeand the thermodynamic analyses have also been estimated. Also, the thermoelectric properties for the both L2 1 and XA structures are examined and discussed based on the Seebeck, electrical conductivity and thermal conductivity coefficients. • FPCs based on GGA(+U) were used to study the magnetoelectronic, elastic, thermal and thermoelectric properties of Co 2 FeGe. • Lattice parameter and bulk modulus of Co 2 FeGe was computed and is agrees with experimental and theoretical calculations. • Band structure and total DOS of Co 2 FeGe compound was investigated. • Thermodynamic properties of Co 2 FeGe were investigated within the quasi-harmonic approximation using Gibbs2 code. • Seebeck coefficient, electrical conductivity, electronic, thermal conductivity, and figure of merit are studied. [ABSTRACT FROM AUTHOR]

The repercussions of an inaccurate account of electronic states near the Fermi level by hybrid functionals in predicting several important metallic properties are investigated. The difficulties include a vanishing or severely suppressed density of states (DOS) at E F , significantly widened valence bandwidth, greatly enhanced electron–phonon (el–ph) deformation potentials, and an overestimate of magnetic moment in transition metals. The erroneously enhanced el–ph coupling calculated by hybrid functionals may lead to a false prediction of lattice instability. The main culprit of the problem comes from the simplistic treatment of the exchange functional rooted in the original Fock exchange energy. The use of a short-ranged Coulomb interaction alleviates some of the drawbacks but the fundamental issues remain unchanged. [ABSTRACT FROM AUTHOR]

In this theoretical study, we have targeted to present the characteristic features of the superconductivity in the cubic A15-type compound Ta 3 Ge by investigating its structural, electronic, elastic, mechanical, phonon, and electron–phonon interaction properties in detail. A critical examination of elastic moduli of Ta 3 Ge reveals that it is soft (ductile) due to significant metallic bonding. A critical surveying of electronic density of states reveals that Ge electronic states make negligible additive to the main valence band region of Ta 3 Ge while its transition metal d states dominate this region. An examination of our phonon results indicate that the low-frequency optical phonon branches and three acoustic phonon branches of Ta 3 Ge are mainly dominated by the vibrations of Ta atoms. Thereby, their d states and their vibrations become the main actors of the transition from the normal state to the superconducting state for Ta 3 Ge. From the integration of the Eliashberg spectral function of Ta 3 Ge, the values of average electron–phonon coupling parameter and logarithmically averaged phonon frequency are found to be 1.08 and 123.05 K, respectively, producing its superconducting temperature T c = 8.3 K, being in good accordance with the experimental value of 8.0 K. • Ta 3 Ge compound is mechanically stable according to the Borns stability conditions. • The main contributions to the value of N(E F) comes from the Ta atoms. • Since there are no negative phonon modes, cubic Ta 3 Ge is dynamically stable. • The calculated λ value is 1.08 indicates a strong coupling strength for Ta 3 Ge. • The calculated T c of 8.3 K for Ta 3 Ge coincides with the experimental value of 8.0 K. [ABSTRACT FROM AUTHOR]

To assess the effects of pseudopotentials and exchange-correlation functionals on trigonal to face-centered cubic phase transition of LaH 10 , we performed density functional theory based first-principles calculations by employing three-types of pseudopotentials with LDA (local density approximation) and GGA (generalized gradient approximation) exchange-correlation functionals. We found that the lattice parameters such as cell angle or cell volume and phase transition pressure exhibit a significant variation with LDA and GGA functionals whereas they exhibit a weak dependence on the pseudopotentials. In general, LDA calculations result in a lower phase transition pressure than GGA calculations. We also investigated the effects of pseudopotentials and exchange-correlation functionals on the electronic properties by calculating the total and partial density of state functions for face-centered cubic phase of LaH 10 at 150 GPa. Computed electronic densities of states at the Fermi level are found to exhibit a weak dependence on the exchange-correlation functionals. • Lattice properties of LaH 10 exhibit a strong dependent on the exchange-correlation functionals. • Trigonal to cubic phase transition pressure also exhibits a strong dependent on the exchange-correlation functions. • Computed density of state functions exhibits a weak dependence on the exchange-correlations. [ABSTRACT FROM AUTHOR]

Carbon nanobuds (CNBs), a novel carbon nanostructure, can be engineered by attaching C 60 (buckyballs) onto the sidewall of a single-walled carbon nanotube (SWCNT). Density functional theory (DFT) calculations are used to investigate the structural, electronic and mechanical properties of armchair (6, 6) and zigzag (10, 0) CNBs. Based on an electronic density of states (DOS) plot, we observed that all CNBs are semiconducting regardless of whether the original SWCNT base is metallic or semiconducting. Our results also indicate that the C-C distances in the C 60 molecule and SWCNTs around the attachment region are increased significantly from the original distance. Furthermore, we also observed that the Young׳s modulus of the CNBs decreased when attaching a fullerene C 60 molecule on the surface of zigzag and armchair SWCNTs. In addition, we demonstrate that the Young׳s modulus of (10, 0) CNB is lower than that of (6, 6) CNB. [ABSTRACT FROM AUTHOR]

Ab initio calculation based on density functional theory was performed for studying high-pressure effects on the electronic properties and photoabsorption of Ga 1− x Mn x As. Mn atom was substituted into the varied GaAs super cells, which observed the Mn concentrations at 3.70%, 8.33% and 12.50%. In zinc blende phase of Ga 1− x Mn x As, we found that the effects of Mn on GaAs in the pressure range 0–10 GPa are the reducing of band gap, generating of impurity peak and increasing of photoabsorption coefficient. The impurity peaks in Ga 1− x Mn x As decrease under pressure increasing because the carriers were excited to conduction band by the effect of bond lengths reducing. The tendency of absorption coefficient of Ga 1− x Mn x As in range of light-wavelength depends on size of impurity peak. [ABSTRACT FROM AUTHOR]

Two contradictory phase diagrams have dominated the literature of high- T c cuprate superconductors. Does the pseudogap line cross the superconducting T c -dome or not? To answer, we have revisited the experimental magnetic susceptibility and knight shift of four different compounds, La 1 − x Sr x CuO 4 , Bi 2 Sr 2 Ca 1 − x Y x Cu 2 O 8 , Bi 2 Sr 2 CaCu 2 O 8 + y , YBa 2 Cu 3 O 6 + y , as a function of temperature and doping. The susceptibility can be described by the same function for all materials, having a magnetic and an electronic contributions. The former is the 2D antiferromagnetic (AF) square lattice response, with a characteristic temperature of magnetic correlations T m a x. The latter is the 'Pauli' term, revealing the gap opening in the electronic density of states at the pseudogap temperature T ∗. From precise fits of the data, we find that T m a x (p) decreases linearly as a function of doping (p) over a wide range, but saturates abruptly in the overdoped regime. Concomitantly, T ∗ (p) is linear and tangent to the dome, either crossing or approaching T m a x (p) at the top of the dome, indicating a qualitative change of behavior from underdoped to overdoped regimes. Contrary to the idea that the pseudogap terminates just above optimal doping, our analysis suggests that the gap exists throughout the phase diagram. It is consistent with a pseudogap due to hole pairs, or 'pairons', above T c. We conclude that T m a x , reflecting the AF magnetic correlations, has often been misinterpreted as the pseudogap temperature T ∗. • Two temperature scales emerge from our analysis : the pseudogap T ∗ and the AF correlation T m a x. • The pseudogap T ∗ exists in the full doping range of the T c -dome. • Our results are compatible with hole pairs above T c up to T ∗. • A change in behavior exists near optimal doping, above the crossing point of T ∗ (p) and T m a x (p) lines. • In conclusion, the T m a x (p) line has been often misinterpreted as the pseudogap temperature. [ABSTRACT FROM AUTHOR]

Abstract: Twisted bilayer graphene (tBLG) is a two-graphene layers system with a mismatch angle between the two hexagonal structures. The interference between the two rotated layers generates a superlattice with a -dependent wavevector that gives rise to van Hove singularities in the electronic density of states and activates phonons in the interior of the graphene Brillouin zone. Here we review the use of Raman spectroscopy to study tBLG, exploring the -dependent effects, corroborated by independent microscopy analysis. The phonon frequencies give a Raman signature of the specific tBLG, while their linewidths provide a straightforward test for tBLG structural homogeneity. Rich resonance effects, including single and multiple-resonances, intra- and inter-valley scattering events make it possible to accurately measure the energy of superlattice-induced van Hove singularities in the electronic joint density of states, as well as the phonon dispersion relation in tBLG, including the layer breathing vibrational modes. [Copyright &y& Elsevier]

Abstract: The crystallographic structure and stability of the phase relative to the and phases in Ti–x M (M=Ta, Nb, V, Mo) alloys are investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. We show that, with increasing concentration of the alloying elements, the structure of the orthorhombic- phase evolutes from the hcp- to the bcc- phase, i.e., the lattice parameters b/a and c/a as well as the basal shuffle y decreases from those corresponding to the phase to those of the phase. The compositional and phase boundaries are determined by comparing the total energies of the phases. The predicted phase boundaries are about 10.2, 10.5, 11.5, 4.5at% for Ti–V, Ti–Nb, Ti–Ta, and Ti–Mo, respectively, in reasonable agreement with experiments. The phase boundaries are higher than the experimental values, possibly due to the absence of temperature effect in the first-principles calculations. Analyzing the electronic density of states, we propose that the stability of the phase is controlled by the compromise between the strength of the covalent and metallic bonds. [Copyright &y& Elsevier]

Abstract: The specific heat of a two dimensional repulsive Hubbard model with local interaction is investigated. We use the two-pole approximation which exhibits explicitly important correlations that are sources of the pseudogap anomaly. The interplay between the specific heat and the pseudogap is the main focus of the present work. Our self-consistent numerical results show that above the occupation , the specific heat starts to decrease due to the presence of a pseudogap in the density of states. We have also observed a two peak structure in the specific heat. Such structure is robust with respect to the Coulomb interaction U but it is significantly affected by the occupation n T . A detailed study of the two peak structure is carried out in terms of the renormalized quasi-particle bands. The role of the second nearest neighbor hopping on the specific heat behavior and on the pseudogap is extensively discussed. [Copyright &y& Elsevier]

Anti-perovskite nitride material F e 3 A l N is studied by using the density functional theory with generalized gradient approximation (GGA+U) approaches and the Monte Carlo simulation in the framework of the Ising model. The parameter of the unit cell has been optimized, the electronic band structure, the electronic density of states and the magnetic moments of the compound are discussed. Based on the energy calculations, the exchange interactions and the magnetic anisotropy are calculated in order to perform the Monte Carlo simulation. Therefore the obtained Curie temperature T c =780 (K) of the compound is in agreement with the experimental one T c =770 (K). The magnetic and magnetocaloric properties are also investigated, the maximum entropy change and the RCP values are 3.355 J/Kg.K and 638 J/Kg for h=5T, respectively. Based on the hysteresis loops, the energy product BH was calculated. The obtained B H m a x is equal to 1.26 (MGOe) above the ambient temperature. These results show that the F e 3 A l N compound can be a good candidate for both information storage applications and magnetic refrigeration. • The magnetocaloric effect, electronic and magnetic properties of AlFe3N have been investigated. • Exchange coupling and magnetic anisotropy have been calculated. • Magnetic energy product of AlFe3N has been discussed. • Based on its relative cooling power, AlFe3N is a good candidate for the magnetic refrigeration. • Based on the magnetic energy product, AlFe3N is a hard magnet material. [ABSTRACT FROM AUTHOR]

The gap modulation by effectively external control is an intriguing feature of the black phosphorene which may enable a flexible design and optimization of electronics. In this paper, combined electric field and external strain effects are systematically investigated to tailor the electrical properties of bilayer black phosphorene (BP) in four stacking order by using density functional theory (DFT). The electronic structures and density of states of bilayer black phosphorene can be modulated by the two external controls, the direct semiconductor-indirect semiconductor-metal transitions emerge under uniaxial in-plain strains and vertical electric field. The band gap is more likely to be modulated by the electric field under compressive strain along armchair direction for the AB stacking structures. The greater the compressive strain, the gap closed at a lower electric field. The partial density of states (PDOS) shows the energy band was mainly contributed by p orbital, and the partial charge density of the VBM and CBM further indicates the shifting trend of electrons and holes between the double layers. Our results provide potential reference information for nano-electronic and optoelectronic applications. • We consider the combination effect of in-plain external force and vertical electric field in bilayer phosphorene. We adopt PBE-TS-DFTD method for structure optimization. • Four stacking orders are considered comprehensively, both the armchair and zigzag direction of the applied in-plain strain are considered. • We report a different modulation effects between compressive force and tensile force under electric field. The direct semiconductors to indirect semiconductors turning points are discussed. • Detailed partial charge density of the VBM and CBM explains the mechanism. [ABSTRACT FROM AUTHOR]

High-entropy ceramics have recently attracted considerable attentions because of excellent combination of exceptional properties. In this work, the temperature dependent elastic properties of (ZrTaNbTi)C have been systematically studied from the density functional perturbation theory combined with self-consistent quasi-harmonic approximation. High entropy ceramic (ZrTaNbTi)C is thermodynamically stable due to the negative formation enthalpy, and is also mechanically stable from the obtained elastic properties. The phonon dispersion relation computed at equilibrium volume contains no imaginary-frequency, implying the dynamical stability. At 0 K, (ZrTaNbTi)C possesses evidently high elastic moduli and hardness. The calculated electronic density of state and Bader charge at 0 K and 2000 K show that (ZrTaNbTi)C have covalent characteristics accompanied by ionic feature while the covalency decreases and the ionicity increases as temperature increases. The temperature-dependent elastic properties show that (ZrTaNbTi)C is mechanically stable in temperature range studied, and remains high strength and hardness at high temperature due to the slight softening of strong covalent bonding. Poisson's ratio, Pugh's ratio and Cauchy pressure suggest the higher brittle-ductile transformation trend as the temperature increases. Moreover, (ZrTaNbTi)C shows less anisotropy at higher temperature from the Zener index A Z and three-dimensional projections, being beneficial to reduce cracking and improve durability. The present study provides more insight into the high temperature behavior of mechanical properties, would be valuable for understanding and design of high-temperature properties of high entropy carbide ceramics. • (ZrTaNbTi)C is thermodynamically, mechanically and dynamically stable. • At 0 K, (ZrTaNbTi)C possesses evidently high elastic moduli and hardness. • (ZrTaNbTi)C remains high strength and hardness at high temperature. • The brittle-ductile transformation trend is stronger as the temperature increases. • (ZrTaNbTi)C shows less anisotropic at higher temperature. [ABSTRACT FROM AUTHOR]

In this paper, particle-swarm optimization algorithms combined was used to investigate the stable VH 2 phases in the pressure range between 0 and 300 GPa. Based on these phases, the structural evolution, lattice dynamics, electronic and thermal properties are discussed. Results show these phases are stable in energy, mechanics and thermodynamics. Study of the electronic density of states show they are all conductors with metallic property and are mainly made up from ionic bonds. Thermal properties show several atmospheric and high pressure VH 2 phases have high Debye temperature, which indicates that they may have an important potential application in high temperature fields. • We predicted the atmospheric and high pressure phases for VH 2 in the range of 0–300 GPa. • Electronic properties and Poisson ratio are calculated to discuss the chemical bonds of predicted structures. • Our predicted VH 2 phases all have high Debye temperatures. [ABSTRACT FROM AUTHOR]

High Z T value and large Seebeck coefficient have been reported in the nanostructured Fe-doped Si–Ge alloys. In this work, the large Seebeck coefficient in Fe-doped Si–Ge systems was qualitatively reproduced from the computed electronic density of states, where a hybrid functional, HSE06, was used for an exchange-correlation functional, as well as a special quasi-random structure (SQS) for a disordered atomic configuration. Furthermore, by replacing Fe with other transition metals, such as Mn, Co, Ni, Cu, Zn, and Au, a dopant that produces a large Seebeck coefficient in Si–Ge alloy systems was explored. It was found that the Mn-doped system produces a large Seebeck coefficient comparable with the Fe-doped system. • Hybrid functional DFT is used to calculate Seebeck coefficient of SiGe alloys. • The investigation is applied to transition metal (Mn, Co, Fe, Ni, Cu, Zn, Au) doping. • Large Seebeck coefficient in Fe-doped SiGe systems was qualitatively reproduced. • Impurity states at band-edges of Fe-doped SiGe boost the Seebeck coefficient. • Large Seebeck coefficient is also found in Mn-doped SiGe due to these impurity states. [ABSTRACT FROM AUTHOR]

We systematically investigate the structural, electronic properties of bulk CeO 2 , its H-phase and T-phase monolayers, studied using first-principles calculations based on density functional theory (DFT). The calculated electronic bandgap is 2.02 eV, 0.86 eV and 2.52 eV for CeO 2 bulk, H-phase and T-phase, respectively. Here, the bandgap is tuned by applying triaxial tensile strain up to 28%. Using strain engineering, the bandgap further increases and behaves as a metal at about 28% for the bulk as well as its monolayers. It is found that for bulk CeO 2 , initially, the bandgap increases for strains up to 16% and then decreases. Similarly, for H-phase the bandgap increases initially at 4% strain and then decreases. Whereas, for T-phase, on applying strain the band gap decreases. Here, the bandgap is in visible range due to that it will be used in optoelectronic devices such as solar cells and LEDs. The result also shows that the CeO 2 nanostructures have diverse electronic properties, tunable by strain engineering and have wide applications in nanoelectronics and nanodevices. • Electronic Band structure for the bulk CeO 2 , its 2D H-phase and T-phase monolayers. • Electronic density of states of bulk, 2D H-phase and T-phase of CeO 2. • Change in energy bandgap on application of triaxial tensile strain for bulk CeO 2 , 2D H-phase and T-phase monolayer. [ABSTRACT FROM AUTHOR]