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Paper is an important material for many applications. During the centuries, it has been the most widely used writing support and therefore paper degradation is a major issue for cultural heritage. The main component of paper is cellulose, one of the most abundant biomaterials on Earth. Cellulose oxidation is mainly responsible for the yellowing of the ancient samples, through the formation of chromophores. In order to investigate this issue and the chromophores' role, we exploit the optical properties combining non-destructive experiments and theoretical calculations based on ab-initio techniques. In this paper, we illustrate the method and show its application to three ancient paper samples. The procedure we describe is a precious tool for cultural heritage preservation: indeed, the approach we present is based on non-invasive and non-destructive measurements that allows a microscopic understanding of cellulose-based artifacts degradation. [ABSTRACT FROM AUTHOR]

Obtaining a reliable positive‐type (p‐type) GaN semiconductor is difficult because of the unipolarity of GaN. This difficulty is one of the bottlenecks restricting the development of GaN‐based optoelectronic devices. To address this problem, this paper adopted the method of generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential based on the framework of density functional theory to construct Ga35MN36, Ga34MN36, and Ga34MHiN36 (M = Be/Mg/Ca; Hi = interstitial hydrogen) models. Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models were also constructed. Results of our calculations indicated that the Ga35MN35 and Ga35MHiN35 (M = Be/Mg/Ca) models cannot achieve a p‐type doping system. Furthermore, the formation energy of Ga34MN36 and Ga34MHiN36 (M = Be/Mg/Ca) systems was greater under Ga‐rich conditions than that under N‐rich conditions, indicating that both doping systems more readily formed and had a more stable structure under N‐rich conditions. Moreover, the formation energy of Ga34MHiN36 (M = Be/Mg/Ca) system was lower than that of Ga34MN36 (M = Be/Mg/Ca) system, and the existence of interstitial H proved to be beneficial to the improvement in system stability. The Ga34CaHiN36 system had the largest hole mobility and the best conductivity. Therefore, the Ga34CaHiN36 system is an ideal material for the application of conductive GaN devices. This study provides guidance into the preparation of p‐type conductive GaN materials. [ABSTRACT FROM AUTHOR]

Using hybrid density functional calculations, this paper systematically investigated the common defects in m-HfO2 and [ABSTRACT FROM AUTHOR]

In this paper, we propose a new numerical method to find the ground state energy of a given physical system within the Kohn–Sham density functional theory. The h‐adaptive finite element method is adopted for spatial discretization and implemented with matrix‐free operator evaluation. The ground state energy is found by performing unconstrained minimization with non‐orthogonal orbitals using the limited memory Broyden–Fletcher–Goldfarb–Shanno (BFGS) method. A geometric multigrid preconditioner is applied to improve the convergence. The clear advantage of the proposed approach is demonstrated on selected examples by comparing the performance to other methods such as preconditioned steepest descent minimization. The proposed method provides a solid framework toward O(N) complexity for the locally adaptive real‐space solution of density functional theory with finite elements. [ABSTRACT FROM AUTHOR]

This paper presents a study on structural and electronic properties of bulk polypropylene – one of the fastest growing engineering plastics – based on density‐functional calculations. The use of recently developed non‐local van der Waals functionals to approximate the exchange–correlation energy is crucial for a good description of structural properties. Various types of chemical imperfections, their impacts on electronic properties of polypropylene are also studied. [ABSTRACT FROM AUTHOR]

In this paper, first principles calculations based on density functional theory were used to study the electronic properties and adsorption behavior of modified rutile surfaces with neutral element dopants (Si, Ge, Sn). The results showed that Sn doped surface has the smallest work function (7.07 eV) and Ge doped surface has the lowest conduction band edge (1.28 eV). Furthermore, the adsorption behavior of H2O and Arg‐Gly‐Asp (RGD) molecules on modified rutile surfaces was calculated to estimate the biocompatibility of modified dental implant surfaces. For the purpose of simulating the real solution environment, the free energy of solvation for adsorbates, calculated by Gaussian 09 program code, was taken into account. The results of the adsorption calculations of H2O indicate that Sn doped surface has a more negative adsorption energy (−3.15 eV) and a higher charge transfer (−0.1) than any other modified surface, which is consistent with its low work function. The results of the adsorption calculations of Arg‐Gly‐Asp demonstrate that Ge doped surface also has a shorter distance (1.95 Å) between Ti atom and O atom in RGD, which is similar with the partial density of states results. All of the results show that the electronic structure of an implant surface has a significant influence on its bioactivity and is also useful for the design of modification methods on dental implant surfaces. [ABSTRACT FROM AUTHOR]

Physical properties of a nano structure are dramatically affected by its surface reconstruction and quantum confinement. For a core/shell structured nanowire (NW), the core/shell interface also plays a key role. The effects induced solely by the surface reconstruction can be estimated by using a reference model in which the dangling bonds on the NW's surface are saturated by a number of pseudo hydrogen atoms with fractional charge. We present in this paper a first principles study on the role of the surface reconstruction in several series of gallium nitride/aluminum nitride core/shell structured NWs. We also show that the model of pseudo hydrogen atoms does suppress the effects of surface reconstruction on both structural and electronic properties of the NWs, thus the model can be used to estimate the role of surface reconstruction. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a reaction graph-based analysis method to study the mathematical structure and dynamical behavior of thin-film deposition reaction network models. Using this approach, we identify reaction network invariants and determine the chemical significance of these conserved modes for thin-film deposition reaction mechanisms. Furthermore, the species-reaction graphs can be used to distinguish “proper” from problematic reaction networks during the initial stages of reaction kinetic modeling studies. Results are presented in the context of a titania deposition process where the transition from atomic layer deposition to chemical vapor deposition growth modes is observed. [ABSTRACT FROM AUTHOR]

In the present paper, density functional theory (DFT) based first-principles methods are applied to investigate the mechanical and bonding properties of the newly synthesized T2 phase superconductor Ta5GeB2 for the first time. The calculated lattice constants are in reasonable agreement with the experiment. The elastic constants ( Cij), bulk modulus ( B), shear modulus ( G), Young's modulus ( Y), Poisson's ratio ( v), Pugh ratio ( G/ B), and elastic anisotropy factor A of Ta5GeB2 are calculated and used to explore the mechanical behavior of the compound. To give an explanation of the bonding nature of this new ternary tetragonal system, the band structure, density of states, and Mulliken atomic population are investigated. The estimated Debye temperature and Vickers hardness are also used to justify both the mechanical and bonding properties of Ta5GeB2. [ABSTRACT FROM AUTHOR]

This paper investigates the geometrical, electronic, and optical properties of a Ga24N24H46 nanoparticle using Density Functional Theory (DFT). The results show that this nanoparticle maintains geometrical parameters very similar to those of the GaN crystal, although it was noticed that the bond length along the direction [0001] of the Ga24N24H46 nanoparticle is smaller than those of the base of the tetrahedron, which is the opposite of what occurs in the crystal. The bandgap of the passivated nanoparticle calculated with DFT is greater than that of the crystal, while an estimate for the hydrogen-free Ga24N24 structure shows a much lower bandgap, in accordance with the literature. The simulation of the optical absorption spectra via Time-Dependent DFT allowed the association of the spatial shape of electronic orbitals with particular transition energies. The highest occupied (HOMO) and lowest unoccupied (LUMO) electronic levels are located on the (0001) and (000-1) surfaces of the particle, respectively, showing that the passivation of GaN nanoparticles should maintain its known photocatalytic activity, and that transition probability between those surface states is relatively low as compared to the HOMO-4 and LUMO transitions at 4.16 eV. Results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we present results concerning ab initio calculations of the optical properties of group IV two-dimensional sheets and compare them with the prediction of an analytical model for excitons in two dimensions, which we explicitly derive. This comparison helps to understand the physics at the basis of the strong many-body effects present in the optical spectra of this class of materials. Although it demonstrates the need of full ab initio calculations for an accurate description of the two-dimensional excitons, it validates, at the same time, this simple approach to estimate, through a density functional theory calculation of the two-dimensional electronic and optical properties, the binding energy and the radius of the excitons in this class of materials. [ABSTRACT FROM AUTHOR]

Cd1− xZn xS solid solutions have drawn much attention for the extensive potential applications. In this paper, we systematically computed the lattice constant, mixing enthalpy and bandgap for each configuration of zinc-blende (ZB) and wurtzite (WZ) type Cd1− xZn xS ( x = 0, 0.25, 0.5, 0.75, 1) solid solutions using the first-principles method, and quantitatively revealed that the Zn-S bond was the most critical factor in determining the relative stability among different configurations with the same composition, as well as the order of the bandgap. Using the configuration-averaged method, the average values of these properties, as well as the optical bowing coefficient, were obtained. We estimated the influence of the configuration average on these quantities, indicating that the configuration average significantly affected the mixing enthalpy, which explicitly determined the phase stability of the solid solutions. [ABSTRACT FROM AUTHOR]

Time-dependent quantum transport parameters for graphene nanoribbons (GNR) are calculated by the hierarchical equation of motion (HEOM) method based on the nonequilibrium Green's function (NEGF) theory [Xie et al., J. Chem. Phys. 137, 044113 (2012)]. In this paper, a new initial-state calculation technique is introduced and accelerated by the contour integration for large systems. Some Lorentzian fitting schemes for the self-energy matrices are developed to effectively reduce the number of Lorentzians and maintain good fitting results. With these two developments in HEOM, we have calculated the transient quantum transport parameters in GNR. We find a new type of surface state with delta-function-like density of states in many semi-infinite armchair-type GNR. For zigzag-type GNR, a large overshooting current and slowly decaying transient charge are observed, which is due to the sharp lead spectra and the 'even-odd' effect. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel semi-analytical approach to calculate first-order electron-vibration (EV) coupling constants within the framework of density functional theory. It combines analytical expressions for the first-order derivative of the Kohn-Sham operator with respect to nuclear displacements with coupled-perturbed Kohn-Sham theory to determine the derivative of the electronic density matrix. This allows us to efficiently compute accurate EV coupling constants.We apply our approach to describe inelastic electron tunneling (IET) spectra of metallic and molecular junctions. A gold junction bridged by an atomic chain is used to validate the developed method, reproducing established experimental and theoretical results. For octanedithiol and octanediamine single-molecule junctions, we discuss the influence of the anchoring group and mechanical stretching on the IET spectra. [ABSTRACT FROM AUTHOR]

Ultrathin Bi films have been theoretically predicted to be an elemental two-dimensional topological insulator recently. Investigation on phonon properties in topological insulators, especially down to a few-layer regime, is an interesting topic. In this paper, the evolution of structures and phonon properties of ultrathin Bi (111) films with thickness is studied from first-principles calculations by including spin-orbit coupling. The calculations of lattice dynamics show that both two Raman modes A1g and Eg in ultrathin Bi (111) films harden compared with those in bulk, which is contrary to other nanomaterials. The possible origin of this anomalous phonon behavior is discussed by considering the peculiar semimetallicity of Bi. With increasing thickness, the frequencies of these two Raman modes decrease gradually toward the values in the bulk. Our calculations also show that the softening and hardening of surface phonon modes coexist in ultrathin Bi films. [ABSTRACT FROM AUTHOR]

Herein, a mechanism is proposed as to how thin films formed from a Heusler compound can simultaneously have both perpendicular magnetic anisotropy (PMA) and be half‐metallic. It is proposed that a thin film formed from a half‐metallic full‐Heusler or half‐Heusler compound that is cubic in the bulk can undergo a tetragonal distortion by adopting the lattice constant of the underlayer material during the thin film deposition process. The value of this distortion can be tuned by using underlayer materials with different in‐plane lattice constants. The distortion can thereby be optimized so that it is large enough to give rise to sufficient PMA, while, simultaneously, small enough to retain the half‐metallic properties (and, therefore, high tunneling magnetoresistance properties) of the Heusler compound. Density functional theory (DFT) calculations that are carried out for 90 full‐Heuslers and 147 half‐Heuslers that have been identified in the literature as half‐metals show that of these, 14 full‐Heusler and 59 half‐Heusler compounds display both half‐metallicity and PMA for optimal tetragonal distortions. [ABSTRACT FROM AUTHOR]

Half‐Heusler alloys offer a variety of applications in the field of electronics and superconductors. They are suitable for the formation of thermoelectric materials and superconductors. Their stupendous applications arouse curiosity among many researchers. Therefore, in this paper, a systematic study of structural, electronic, and vibrational properties has been done using density functional theory and density functional perturbation theory. The structural properties such as lattice constant, bulk modulus, and pressure derivative of bulk modulus have been calculated. Electronic and bonding properties have been examined from electronic band structure, charge density contours, and Fermi surfaces. The phonon dispersion spectra and phonon density of states for LuPdBi are reported and discussed for the first time. Moreover, the eigenvector displacements for optical phonons at the zone center are also described to support the reliability of phonon calculations. The computation of phonon spectra disclosed the fact that the resulted phonons are real. Real frequencies of phonons are witness of alloy stability in the cubic phase. The superconducting properties have also been evaluated by employing electron–phonon interaction and Eliashberg theory. The Coulomb pseudopotential variable µ* is selected to be 0.11 and the computed value of transition temperature is found to be Tc = 1.802 K. This value of Tc is in agreement with the experimental value of Tc = 1.80 K. [ABSTRACT FROM AUTHOR]

By means of DFT calculations, we have individuated a minimum-energy path connecting two energy minima of clean graphene on clean and relaxed oxygen-terminated (0001)'SiO [ABSTRACT FROM AUTHOR]

The goals of this study are to use density functional theory to study the core structure energetics of the 30° and 90° partial dislocations in HgTe, CdTe, and Hg0.7Cd0.3Te as well as the density of states of these dislocations in CdTe and Hg0.7Cd0.3Te. For the 30° partial dislocations, two stable dislocation pairs were found. The pair with a double‐periodic α‐core (Te) dislocation and a single‐periodic β‐core (Hg/Cd) dislocation was found to be the most stable out of the two for the simulation sizes tested. For the 90° partial dislocations, two stable dislocation pairs were also found. The first has a single‐periodic β‐core dislocation and a single‐periodic α‐core dislocation, whereas the second has a double‐periodic β‐core dislocation and a single‐periodic α‐core dislocation. The most stable out of the two depends on the simulation size tested. For both of these partial dislocations in Hg0.7Cd0.3Te, it was found that it is energetically favourable for Hg atoms to segregate to the dislocation cores. Furthermore, in CdTe and Hg0.7Cd0.3Te, it was found that the 90° partial dislocations are likely to be more detrimental to the material optoelectronic properties since they introduce more mid‐gap states within the band gap in comparison to the 30° partial dislocations. [ABSTRACT FROM AUTHOR]

A promising strategy to tailor the magnetic and electronic properties of 2D van der Waals magnets is to integrate them with a ferroelectric (FE) substrate. Herein, the FE substrate effect of BiFeO3(0001) with different surface terminations is explored using density functional theory calculations for the ferromagnetic 2H‐VS2 monolayer. It is observed that depending on the polarization direction and surface termination of the BiFeO3(0001) FE substrate, the 2H‐VS2/BiFeO3(0001) interface exhibits a substantially varied charge transfer behavior. The magnetic and electronic properties of the monolayer 2H‐VS2 are significantly modulated by the interface charge transfer. Furthermore, in the 2H‐VS2/BiFeO3(0001) heterostructures, large interface magnetoelectric coupling coefficients are predicted. The in‐plane magnetic and electronic properties of monolayer 2H‐VS2 can be effectively tuned by the out‐of‐plane FE polarization, paving the way for a novel class of spintronic devices based on the 2H‐VS2/BiFeO3(0001) hybrid system. [ABSTRACT FROM AUTHOR]

Cluster‐based crystals containing the (Nb6Cl12)2+ or (Ta6Cl12)2+ clusters, including the well‐known Nb6Cl14, K4Nb6Cl18, and the Prussian blue analog (Me4N)2 [MnNb6Cl12(CN)6], have been investigated by density functional theory. The electronic structure of the cluster is the same for all compounds, with a semiconducting gap of around 1 eV between occupied and empty states, in the range of interest for solar energy applications. Calculations suggest that these clusters could be used as cations in hybrid organic–inorganic perovskites, as a substitute for toxic Pb2+. Moreover, bandgaps, band alignment, and hydrogen adsorption calculations show that the designed cluster‐based hybrid perovskites have potential as intermediate band materials for photovoltaics, and as photocatalysts for the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Combining bond–band–barrier (BBB), density‐functional theory (DFT) and zone‐selective electron spectroscopy (ZES) correlations, we investigate the bonding mechanisms at Na/Ta(110) and Ta/Na(110) interfaces. When the Ta metal coverage on the Na(110) surface is increased from 7/9 ML to 8/9 ML, the Ta surface distribution changed from one‐dimensional chains to two‐dimensional ring structures. Moreover, the Ta‐induced shifts in the surface binding energy (BE) on the Na(110) surface were dominated by quantum entrapment, whereas the Na‐induced shifts in the BE on the Ta(100) surface are dominated by polarization. DFT calculations reveal that the Ta atomic chain is more stable than the structure of the Ta atomic ring. The adsorption of Ta atoms on the Na(110) surface is more stable than the structure of the Na atoms adsorbing on the Ta(110) surface. The 1D chain formations and 2D ring structures on the Na(110) surface are identified and explained in this paper. [ABSTRACT FROM AUTHOR]

Herein, AlnTin (n = 2–12) clusters are studied by density‐functional theory method. The evolution of the geometric structure shows that Ti atoms tend to gather inside the clusters. The analysis of the relative stability and highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap show that AlnTin (n = 2–12) clusters tend to be stable and the bonding probability increases when n > 8. Nature bond orbitals (NBO) results show that the strong d‐orbital effect between Ti atoms results in the formation of TiTi bonds more easily than AlTi bonds, which leads to the enrichment of Ti atoms inside the AlnTin (n = 2–12) clusters. When n ≥ 8, Al atoms that surround the core formed by Ti atoms tend to form stable triangular configuration, which is stable adsorption site for Al atoms. Herein, the grain‐refining effect of TiAl3 grain refiners in Al alloys at the atomic level can be explained. [ABSTRACT FROM AUTHOR]

Electron–electron interactions on the Si (111) surface associated with inaccuracies in treating exchange and correlation are shown to be consistent with discrepancies found between density functional calculations and experimental measurements of the 7 × 7 surface. Here, the measured filled and empty surface states of the 7 × 7 surface are shown to be shifted away from one another relative to those predicted by effective one electron calculations using density functional theory. This corresponds to the "energy gap problem" widely known to occur in most bulk semiconductors arising from the approximate treatment of electron exchange–correlation, X–C, within such theoretical constructs. Considering more realistic treatments of X–C to correct these energy shifts leads to a different interpretation of the surface states and a new interaction that stabilizes the 7 × 7. This provides a physical basis for its unusual properties some of which are also observed in related 2D systems. The effects of various electron–electron interactions from these new interactions are considered and their behavior is used to explain the metallic nature of the 7 × 7 at 300 K. [ABSTRACT FROM AUTHOR]

Advancement toward opening a bandgap at the Dirac point induced by symmetry breaking paved the way to realize 2D heterostructures with graphene and hexagonal boron nitride (h‐BN). An alternate arrangement of graphene and h‐BN layers in a 3D stacking can tune the bandgaps of these composites depending on the position of B and N atoms with respect to C atoms of graphene. Herein, a unique possibility of arranging graphene and h‐BN atomic layers in a quasiperiodic Fibonacci sequence to study the possibilities of controlling the electronic properties of these heterostructures is explored. Density functional theory calculations combined with van der Waals corrections reveal that these quasiperiodic heterostructures are more stable than normal periodic stacking of monolayers of graphene and h‐BN. Moreover, for certain arrangements of atomic layers, sizeable bandgaps can be obtained. [ABSTRACT FROM AUTHOR]

Based on the density functional theory (DFT) as incorporated in the Wien2k package, the lattice parameters and atomic position of calcium niobate (CaNb2O6) were optimized. Furthermore, the electronic, optical, and structural properties of the relaxed compound were calculated. Relaxed calcium niobate presents a direct band gap with 3.5 eV, which makes it a good candidate for photovoltaic applications. The DFT calculation reveals that the O atoms make the major contributions in the valence band, while Nb and Ca atoms are the dominant contributors in lower and upper portions of the conduction band, respectively. Moreover, the optical properties of compounds such as refractivity, dielectric constant, reflectivity, etc. are calculated and discussed in detail. [ABSTRACT FROM AUTHOR]

Boron arsenate (BAsO4) is a β‐cristobalite‐like material, which crystallizes in the I4¯ space group. However, unlike β‐cristobalite itself, BAsO4 is well characterized and known to be stable and at ambient conditions. This work presents the results of extensive density functional theory (DFT)‐based simulations aimed at elucidating the nanoscale deformations that such crystals undergo when subjected to uniaxial tensile and compressive loads along their crystallographic [001] c‐direction. It is shown that such uniaxial loading results primarily in intra‐tetrahedral deformations rather than their tilting/rotations (which causes the auxeticity in the (001) plane). Through their analysis in isolation from other modes of deformation, this study gives a much better insight into such intra‐tetrahedral deformations and helps explain better the cause of the measured negative linear compressibility in the c‐direction at elevated pressures, which recently has been attributed to a "demi wine‐rack" mechanism caused by the same intra‐tetrahedral deformations. [ABSTRACT FROM AUTHOR]

The study of Raman spectra of recently predicted ultrathin diamond films (diamanes) with nanometer thickness, transformed from multilayered graphenes by the adsorption of hydrogen is presented. Here we studied the phonon spectra of diamane structures in detail by ab initio method, especially the Raman and infrared (IR) vibrational modes. In particular, two-layered diamanes display Raman peaks near 1110, 1260, 1320, 2860 cm−1, and three-layered diamanes have a broad region (1110-1340 cm−1) of Raman shifts and peaks near 2830-2860 cm−1. The spectra are radically distinguished from the similar spectra of one to three layered graphenes and graphane. [ABSTRACT FROM AUTHOR]

Density‐functional‐theory (DFT)‐based, ab initio molecular dynamics (AIMD) simulations of amorphous materials generally suffer from three computer‐resource‐related limitations due to their O(N3) cubic scaling with model system size, N. They are limited to a maximum model size of N ≈500 atoms; they are limited to time scales <1 ns; and, usually, only a single model can be simulated in any one investigation. This article discusses a machine‐learned, linear‐scaling (O(N)), DFT‐accurate interatomic potential (a Gaussian approximation potential, GAP), originally developed by Mocanu et al. [J. Phys. Chem. B 2018, 122, 8998] using a Gaussian process regression method for the ternary phase‐change‐memory material Ge2Sb2Te5 (GST). The chemical transferability of this GAP potential is explored in an application to the case of simulating amorphous models of the phase‐change‐memory and thermoelectric material Sb2Te3, an end‐member of the GST compositional tie‐line GeTe–Sb2Te3. The GAP‐model results are compared with those obtained from conventional DFT‐based AIMD simulations. [ABSTRACT FROM AUTHOR]

First‐principles calculations using density functional theory and two methods in comparison, Quantum ESPRESSO and Siesta, are done on large supercells which describe different placements of two identical adsorbed alkali metal atoms (of either Na or K species) on the monolayer of boron carbide BC3. The energy of single‐atom adsorption over the center of C6 ring, the center of C4B2 hexagon, and over a boron atom are preliminarily estimated, the effect of applying the Grimme D2 correction on the adsorption characteristics is evaluated, and the comparison of these results with available data is discussed. The interaction of two identical Na or K atoms adsorbed at close enough distances (less than ≃10 Å) is negligible if the adsorption occurs at the opposite sides of the BC3 layer, but creates a steep repulsive potential at distances less than ≃8 Å if both atoms are adsorbed on the same side of the monolayer. Relaxation patterns resulting from the two K atoms being trapped at adjacent adsorption sites in the lattice are explained. The results suggest that the density of adsorbed K atoms on BC3 can be interestingly high. [ABSTRACT FROM AUTHOR]

Herein, the effects of Cu doping with different concentrations on the stability, elastic properties, and electronic structure of Mg2Si are investigated by first‐principles calculations based on density functional theory. The research results show that Mg2Si and Mg8−xSi4−yCux+y (x, y) = {(0.125, 0), (0, 0.125), (0.25, 0), (0, 0.25), (0.5, 0), (0, 0.5), (1, 0), (0, 1)} are stable in the system. The Cu atoms tend to preoccupy Mg sites in Mg2Si lattices, and the alloying ability is stronger than that of Mg8Si4−yCuy (y = 0.125, 0.25, 0.5, 1). Although all dopants are brittle phases, the doping behavior of Cu atoms improves the elastic and plastic properties of the Mg2Si alloy system. The bonding modes of the crystal are also changed. The SiCu covalent bond formed by Mg8−xSi4Cux (x = 0.125, 0.25, 0.5, 1) further increases the structure stability. Meanwhile, Mg7Si4Cu and Mg8Si3Cu are changed from semiconducting to metallic state by energy band structure analysis. It not only increases the carrier concentration, but also reduces the free electron transition energy, which improves the conductivity of the intrinsic Mg2Si. These investigations will provide some theoretical basis for the application of Mg2Si intermetallic compounds in structural materials and thermoelectric materials. [ABSTRACT FROM AUTHOR]

Herein, the spin‐dependent transport properties of a zigzag graphene nanoribbon (zGNR) with edges decorated with a fluoranthene group are studied. Atomically perfect zigzag edge, including phenyl‐edge functionalization, was synthesized by Ruffieux et al. in a bottom‐up chemical technique. By performing nearest‐neighbor tight‐binding model in combination with Landauer formalism and Green's function approach, as well as considering Coulomb electronic interaction computed both with density functional calculations and mean‐field approximation of the Hubbard model, the magnetic and spin‐resolved transmissions are studied. Both the model Hamiltonian and density functional theory (DFT) descriptions yield very similar results. Importantly, by generating a special supercell, three different antiferromagnetic alignments for phenyl‐edge zGNR have been calculated, which was not developed in previous studies. The results show that by adding pentagon rings on both sides of the zGNR, the conductance loses its step‐like behavior. Our structure of interest is a semiconductor with a transport gap of 0.56 eV. This kind of defective structure will enable the spin‐feature characteristic, such as spin filtering, and add the spin degree of freedom to graphene‐based logic devices. [ABSTRACT FROM AUTHOR]

The origin of the converse magnetoelectric (CME) effect in the Nb‐doped BaTiO3 (NBTO) polar metal is investigated by density functional theory. Unlike the Fe doping system, where the magnetic moment is chiefly contributed by eg orbitals of the Fe atom, the magnetic moment of the NBTO system is mainly contributed by the dxz/dyz orbitals of Ti (Nb) atoms and highly depends on the polarization intensity. When the in‐plane compressive strain η ≤ −2%, the magnetic moment of the NBTO system is zero because electrons predominantly occupy the dxy orbitals. However, the switching process of the ferroelectric polarization induces a strong CME effect with significant magnetic moment changes. Especially, the magnetic moment changes in the NBTO system with the compressive strain η ≤ −2%, which is dozens of times of that of the unstrained NBTO system. These results are useful for designing new ultrafast and low‐power information storage devices with remarkable electrically controlled magnetism. [ABSTRACT FROM AUTHOR]

First‐principles calculations with the most accurate hybrid functional are used to investigate the effect of native point defects and Ti/Fe impurities on electrical and optical properties of α‐Al2O3. For dominant native point defects, the Al vacancy (VAl), O vacancy (VO), and Al interstitial (Ali) defects are considered, and it is found that only VAl defect provides the absorption line in the visible light region. Regarding Ti‐doped or Fe‐doped sapphire, it is found that their colors should be related to intra‐atomic d–d transitions. For the Ti–Fe pair, it is found that the ground‐state configuration is TiIII–FeIII, and its binding energy is very high, indicating that this pair can exist in high concentration. The calculated optical absorption energy associated with Ti–Fe pair is ≈1.92 and 1.84, which is appropriate for sapphire to be blue. It is, therefore, suggested that the intervalence charge transfer (IVCT) mechanism is the cause of blue color in blue sapphire. [ABSTRACT FROM AUTHOR]

Novel two‐dimensional (2D) tetragonal (tetra‐) CrXB2 (X = Mn, V) sheets are studied using density functional theory (DFT) with Monte Carlo (MC) simulations. Both, tetra‐CrMnB2 and tetra‐CrVB2 sheets exhibit metallic ferromagnetism with great stability at elevated temperatures. The magnetic moment for tetra‐CrMnB2 (1.63 μB per unit cell) and tetra‐CrVB2(0.53 μB per unit cell) sheets are found to be far less than that of pure tetra‐Cr2B2 (6.02 μB per unit cell). Interestingly, an antiferromagnetic–ferromagnetic (AFM–FM) transition occurs as a result of alloying the pure Cr2B2 with Mn and V atoms. The tetra‐CrMnB2 exhibits a sizable magnetic anisotropy energy (MAE) of 136.25 μeV per Mn–Cr atom, larger than that of tetra‐CrVB2 (17.5 μeV per V–Cr atom), and both the sheets prefer out‐of‐plane magnetization. The MAE can be tuned via the application of an electric field for both, tetra‐CrMnB2 and tetra‐CrVB2 cases. MC simulations based on 2D Heisenberg model predict a Curie temperature (TC) of 140 and 20 K for tetra‐CrMnB2 and tetra‐CrVB2 sheets, respectively. These novel 2D sheets hold promise for controllable spintronic devices application. [ABSTRACT FROM AUTHOR]

Investigation of the mechanical, electronic, and thermodynamic properties of recently synthesized (Ta1−xHfx)4AlC3 and (Ta1−xHfx)4Al0.5Sn0.5C3 (0 ≤ x ≤ 0.25) solid solutions is conducted using density functional theory for the first time. The computed lattice constants are in good agreement with prior results. The calculated stiffness constants are used to check the mechanical stability of the studied compositions. The bulk modulus (B), shear modulus (G), and Young's modulus (Y) are found to be influenced by Hf and Sn substitution. The titled solid solutions are brittle in nature. The 3D presentations of elastic moduli and elastic anisotropy factors are used to disclose the anisotropic mechanical features of the considered compositions. The electronic band structure, density of states, and charge density mapping (CDM) show the metallic nature, the contribution from different states to electronic conductivity, and atomic bonding characteristics. The electronic band structure and CDM are also used together to investigate the change in bonding strength due to Hf and Sn substitutions. The Debye temperature (ΘD), minimum thermal conductivity (Kmin), Grüneisen parameter (γ), and melting temperature (Tm) of the studied solid solutions are estimated and analyzed. A good correlation is found between the mechanical and thermodynamic properties. [ABSTRACT FROM AUTHOR]

Herein, the structure and electronic properties of Ti‐doped LiCoO2 have been studied systematically using the first‐principles projector augmented wave (PAW) method based on density functional theory (DFT). The structure is distorted due to the presence of Co2+ after Ti doping. When the concentration of dopant Ti is less than 5.6%, the volume change of unit cell is independent of the Ti‐doped concentration, but at higher dopant Ti concentration, the volume of unit cell increases with increase of dopant Ti concentration. Meanwhile, it is also found that the Li‐ion diffusion rate and electronic conductivity are improved, and the concentration of dopant Ti has little effect on the redox potential. These results can promote Ti‐doped layered Li transition metal oxide cathode materials' studies and improve layered Li transition metal oxide cathode materials design for Li‐ion batteries (LIBs). [ABSTRACT FROM AUTHOR]

The electronic and optical properties of armchair Janus MoSSe/WSSe superlattice nanoribbons (A‐JSLNRs) under strain and electric field are studied by first‐principles calculations. The bandgap of A‐JSLNRs can be dramatically modulated by axial strain and transverse electric field. The optical absorption edge shows an obvious red‐shift trend with the increasing strain, and the absorption peak for the visible light will be enhanced significantly as strain decreases from 8% to −8%. The general rule for the change of the bandgap and the optical absorption tuned by strain is explained well according to the different changes of near‐band‐edge states. Moreover, the transverse electric field will induce a semiconductor–metal transition to the A‐JSLNRs. Based on the results, the electronic bandgap and optical properties of A‐JSLNRs shows sensitivity to the applied strain and external electric field, which can be used to effectively tune the properties of A‐JSLNRs to make them suitable for optoelectronic applications. [ABSTRACT FROM AUTHOR]

The theoretical treatment of complex oxide structures requires a combination of efficient methods to calculate structural, electronic, and magnetic properties, due to special challenges such as strong correlations and disorder. In terms of a multicode approach, this study combines various complementary first‐principles methods based on density functional theory to exploit their specific strengths. Pseudopotential methods, known for giving reliable forces and total energies, are used for structural optimization. The optimized structure serves as input for the Green's function and linear muffin‐tin orbital methods. Those methods are powerful for the calculation of magnetic ground states and spectroscopic properties. Within the multicode approach, disorder is investigated by means of the coherent potential approximation within a Green's function method or by construction of special quasirandom structures in the framework of the pseudopotential methods. Magnetic ground states and phase transitions are studied using an effective Heisenberg model treated in terms of a Monte Carlo method, where the magnetic exchange parameters are calculated from first‐principles. The performance of the multicode approach is demonstrated with different examples, including defect formation, strained films, and surface properties. [ABSTRACT FROM AUTHOR]

Internal structural distortions are of great interest in the determination of electronic and magnetic properties of the strong correlated rare earth manganites. When combined with external structural modifications like uniaxial or biaxial strains, structural distortions can lead to the emergence of new magnetic ground states. This realization is seemingly more probable with the low‐band‐width manganite GdMnO3 on the grounds that it is located in the magnetoelectric phase diagram of orthorhombic rare earth manganites between the A‐type antiferromagnetic (AFM) order and the cycloidal spin orders. Herein, a thorough analysis of the magnetic structure of GdMnO3 based on the density functional theory connected with a classical Heisenberg model together with Monte Carlo calculations is presented. It is found whether a compressive uniaxial strain along the c direction or biaxial strain on the ab plane favors a ferromagnetic (FM) ground state over the AFM one. On the contrary, a tensile strain also on the ab plane is likely to stabilize the E‐type AFM order. [ABSTRACT FROM AUTHOR]

High‐entropy metal diborides (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr) are a new class of ultrahigh temperature ceramics. The novel structural, mechanical, and electronic properties of (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr) are studied within density functional theory, with the compositional disorder being treated using the special quasi‐random structures technique. The elastic stiffness constants Cij, as well as bulk, shear and Young's modulus of (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr) are studied to estimate the mechanical properties. The ductility is also investigated from several criterions, showing that (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr) is still intrinsically brittle. The high Debye temperature of (Hf0.2Zr0.2Ta0.2M0.2Ti0.2)B2 (M = Nb, Mo, Cr) indicates the strong interatomic interactions and good thermal conductivity. The detailed investigations of electronic structure reveal that covalent and metallic bonds are respectively formed in the boron layer and the metal layer, mixed ionic and covalent bonds are formed between the metals and boron interlayer. [ABSTRACT FROM AUTHOR]

The defect structures and electronic properties of orthorhombic elongated (OE) and tetragonal compressed (TC) Rh2+ centers in LiD are theoretically studied using Density Functional Theory (DFT) with the periodic CP2K program. The calculations demonstrate obvious differences in defect structure between the two centers. OE center with one next nearest neighbor (nnn) cation vacancy (VLi) in [100] axis shows the Jahn‐Teller elongation of about 0.076 Å along [001] axis, whereas TC center with one nnn VLi in [001] axis exhibits a compression of about 0.049 Å along this direction. The ligand between the central Rh2+ and the VLi is found to move away from the VLi by about 0.038 or 0.035 Å for O­­E or TC center. The larger magnitude of the overlap population (≈ −0.5907 or −0.5494 e) of the RhD bonds in OE or TC center than that (≈0.2373 e) of the host LiD bonds in pure LiD indicates much stronger covalency of the former. The simulated UV–Vis and electron paramagnetic resonance (EPR) spectra with the embedded cluster model in ORCA code are consistent with the experimental data. The present results are discussed and compared with those of the previous perturbation calculations. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) simulation show that in p‐doped porous silicon (PS), boron (B) atoms are passivated by surface dangling bonds of Si atoms (pb‐centers) at distances up to 25 Å. A positive charge of the pb‐centers leads to the appearance of an increased potential region and a Coulomb blockade (CB) of free holes. When a NO2 molecule is adsorbed on a surface OH group near the pb‐center, a shallow acceptor state arises. This state is related to the NO2 molecule and not to the B atom. When an electron is captured from the valence band by the NO2 molecule, the potential around it and the pb‐center decreases, which removes CB. [ABSTRACT FROM AUTHOR]

The geometrical structure, defect formation energies, electrical and optical properties of C and/or Cr doped anatase TiO2 are calculated by GGA + U method under the framework of density functional theory. The relationship between band structure and light absorption is revealed. The results show that the lattice is obviously distorted after doping, and the stability of C and Cr co‐doping is higher than just Cr doping, second only to Cr doped TiO2. The contribution of C is forming impurity energy levels, and the contribution of Cr is to reduce the band gap in the single doped system. In the co‐doped system, Cr atoms are used as donor impurities and C atoms act as acceptor impurities. The impurity energy is composed of C 2p and Cr 3d orbital hybridization, which reduces the band gap and promotes the separation of the impurity levels. C and Cr co‐doping expands the light absorption of TiO2 to the entire visible region, thereby increasing the absorption coefficient and effectively enhancing the photocatalytic efficiency. [ABSTRACT FROM AUTHOR]

In this work, we focus on the study of the structural, electronic, and elastic properties of beryllium oxide under the influence of both temperature and pressure. Therein, we use the density functional theory (DFT) and quasi‐harmonic Debye model within the general gradient approximation (GGA). The results show that the enthalpy of BeO with wurtzite structure is lower than that with rocksalt structure at 171.74 GPa. Through our calculations, we deliberated the structural (a and c), electronic (band structure and partial density of states), and elastic properties (elastic constants, shear modulus, bulk modulus, and Young's modulus) at high temperature and under different pressures. In addition, we find that our results are in good agreement with previous experimental and theoretical results at P = 0 GPa and T = 0 K. Our results at high temperature and under different pressures can be considered as a new reference for further investigation. [ABSTRACT FROM AUTHOR]

The investigation of the electronic structure of P‐ion implanted TiO2 thin films (E = 30 keV, D = 1 × 1017 cm−2) with anatase structure is performed by X‐ray photoelectron spectroscopy (XPS) measurements (core levels and valence bands) and first‐principles density functional theory (DFT) calculations. It is found that the XPS P 2p‐spectra reveal the presence of two signals at 134.2 and 130.3 eV which can be attributed to the formation of P–O (with P5+ ions) and P–Ti (with P3− ions) bonds, respectively. This means that both cationic (P → Ti) and anionic (P → O) substitution take place in P‐ion implanted anatase thin films. This conclusion is confirmed by DFT calculations which show that the XPS valence band structure of P:TiO2 can be reproduced only under mixed substitution. The presence of two kinds of phosphorus ions (P5+ and P3−) in ion‐implanted TiO2 can be useful for developing new multifunctional advanced materials with configurable properties for a wide range of applications. [ABSTRACT FROM AUTHOR]

It is shown that the hypothesis of reactivation of subsurface boron atoms in porous silicon (PS) by NO2 molecules at their adsorption on the surface dangling bonds cannot explain the reversible increase of free holes concentration in n‐type PS and in p–n junctions with oxidized surface. The alternative model of hole conduction emergence in silicon structures upon adsorption of NO2 molecules is proposed. Density functional theory (DFT) calculations show that fixing NO2 molecules on the hydroxyl groups of silicon or its oxide surface can produce acceptor states and, therefore, free holes. [ABSTRACT FROM AUTHOR]

The accuracy of the theoretical description of materials properties in the framework of density functional theory (DFT) inherently depends on the exchange‐correlation (XC) functional used in the calculations. Here we investigate the influence of the choice of a XC functional (PBE, RPBE, PW91, and PBE0) on the kinetics of the adsorption, diffusion and dissociation of water on the rutile TiO2(110) surface using a combined Kinetic Monte Carlo (KMC) – DFT approach, where the KMC simulations are based on the barriers for the aforementioned processes calculated with DFT. We also test how the adsorption energy of intact and dissociated water molecules changes when dispersion interactions are included into the calculations. We consider the beginning of the water layer formation varying coverage up to 0.2 monolayer (ML) at temperatures up to 180 K. We demonstrate that the dynamics of the simulated water–titania system is extremely sensitive to the choice of the XC functional. [ABSTRACT FROM AUTHOR]

Despite the fact that the Fe-based superconductors (FeSCs) were discovered nearly 10 years ago, the community is still devoting a tremendous effort toward elucidating their relevant microscopic pairing mechanism(s) and interactions. At present, there is still no consistent interpretation of their normal state properties, where the strength of the electron–electron interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for the important high-energy mass renormalizations phenomenologically, and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, many representative FeSCs with Tc < 40 K studied so far are found to belong to an intermediate coupling regime (with the possible exception of some systems near a quantum critical point or in the vicinity of a Lifshitz transition). This finding is in contrast to the generally strong coupling scenarios proposed in the early period of the FeSC history. We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe2As2 (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the ε-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field, pointing to its dominant role in the superconductivity of these three compounds. [ABSTRACT FROM AUTHOR]

Electronic and transport properties of carbon-nanotube (CNT) hybrid junction CNT(3, 3)/CNT(6, 0)/CNT(3, 3) are investigated and compared with substitutionally doped junction with transition metal atoms, iron, cobalt, and manganese; using density functional theory combined with nonequilibrium Green’s function formalism. Transmission coefficient and current–voltage (I–V) characteristics are calculated for all configurations. The results indicate a smooth increase of current with voltage in pristine junction up to 0.75V while in the case of higher voltages, the increase accelerates significantly and the conductance for the voltages between 1 and 1.5 becomes almost constant, about 40μAV. The replacement of carbon atoms with Fe, Co, and Mn in the scattering region causes rather substantial reduction of the transmission and conductance of the hybrid junction. It causes the current to reduce nearly 25% at the voltage of 1.5V compared to the pristine one. It also appears that, there is no serious difference in the I–V characteristics for different impurity atoms, except some deviation in manganese conductance from the other two impurities’ curves. These results can be useful for future CNTs based nano-electronic applications. [ABSTRACT FROM AUTHOR]