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In this paper, the effect of C, N and O atom doping of intrinsic MoSe₂ on the adsorption capacity of Ni is investigated based on first-principle research methods. The aim is to analyze whether intrinsic MoSe₂ can be doped and modified to improve its adsorption capacity of Ni so that it can be used as a new type of adsorbent material. By calculating and analyzing the energy band structure, density of states, differential charge and optical properties of each system, the conclusions are as follows: the O-doped MoSe₂ system has the best adsorption capacity for Ni, and the adsorption capacities of the three systems are in the following order: O>N>C. The bandgap value of intrinsic MoSe₂ adsorbed Ni-atom decreases, while the Fermi energy level of the C-doped MoSe₂ adsorbed Ni-atom system is located in the valence band, which shows p-type doping. The differential charge of the system was analyzed and the charge transfer of the adsorbed system was increased by C, N and O atom doping, and the O-doped system had the strongest adsorption capacity for Ni. It was shown that the charge distribution between the system and the adsorbed Ni-atom changed considerably after atomic doping, and the bonds between the Ni-atom and the dopant atoms of the C-, N- and O-doped adsorption system were strongly ionic. Optical analysis reveals that C, N and O atom doping improves the charge binding ability of Ni-adsorbed MoSe₂ material, which gives it a higher polarization rate and faster electric field response. The absorption of ultraviolet light is greatly enhanced, which can improve the efficiency of solar cells and convert solar energy into electricity more effectively. Overall, the Ni adsorption capacity of atomically doped MoSe₂ is improved, indicating that doping can be an effective means to improve the adsorption of Ni-atom by intrinsic MoSe₂. It is hoped that the research results in this paper can provide some theoretical guidance for the application of MoSe₂ in optoelectronic devices.

A heteroepitaxial growth model of the ZnO film on sapphire (0001) is calculated by using a plane wave ultrasoft pseudo-potential method based on density functional theory. It is found that interfacial atoms have different diffusivity at 400°C, 600°C and 800°C. The temperature has a decisive effect on the surface and interface structures of ZnO/α-Al₂O₃ (0001) and on the growth mode of ZnO thin films. In the whole process of the adsorption and growth of ZnO, the diffusivity of O atoms is higher than that of Zn, and the interlayer diffusion has an important impact on the homogeneous growth of thin films. There are two growth modes of ZnO on sapphire (0001), which is further demonstrated by theoretical calculation. The growth mode at about 400°C has a character of mainly spiral-twisted growth with Zn-hexagonal symmetry structure, and it is favorable for forming the Zn-terminated surface. But in the case of 600°C, a regular in-plane growth is observed, which facilitates the O-terminated surface of the ZnO thin film. It can be observed from the calculation that the vacancies of Zn where the atomic layer is near to the α-Al₂O₃ (0001) surface is more than that of O atoms.

We study systematically the site occupancy and effects of alloying element on NiAl bonds character of 4d transition metals by first-principles method based on density functional theory. The impurity formation energies of 4d TM of NiAl in Al-site and Ni-site are calculated. Y, Zr, Nb, Cd prefer to occupy the Al-site, whereas Mo, Tc, Ru, Rh, Pd, Ag prefers to occupy Ni-site. Crystal distortion and the overlap population between the alloying element and its first-neighboring atoms and are also calculated. The result shows that the substituting Al-site the elements Y, Zr, Nb, Cd interact with its first-neighboring Ni atom by anti-bonding. The total covalent ratio is decreased by theses elements which may improve ductility of NiAl. For Ni-site elements, the interaction between the alloying element Mo (Tc, Ru, Rh, Pd, and Ag) with its first-neighboring atoms Al also shows decrease in covalent. Site occupation of 4d transition metals are also discussed by the reaction energy for formation Ni₂TiX and X bulk phase.

First principles study of the structural, electronic and optical properties of Al-doped γ-Ge₃N₄ with different concentration has been reported using the pseudo-potential plane wave method within the generalized gradient approximation (GGA). The binding energy and the formation energy suggest that Aluminum (Al) impurities prefer to substitute Ge at octahedral sites. Different doping concentrations are considered and the corresponding density of states (DOS) are analyzed. Calculated DOS indicates that there are holes in the top of the valance band after doping, meaning a p-type doping. We study the complex dielectric function, the absorption coefficient, and the electron energy loss spectra. It is demonstrated that for the low Al concentration, the material exhibits the dielectric behavior and for the high Al concentration, the material has possibilities to exhibit some metallic behavior. The γ-Ge₃N₄ doped with Al has a much higher static dielectric constant than undoped γ-Ge₃N₄, implying its potential applications in electronics and optics.

First-principles calculations have been conducted to study the electronic structures and optical properties of 2Al- and 2Ca-doped β-Si₃N₄. Calculated formation energies of 2Al- and 2Ca-doped systems are 5.9745 eV and 18.9376 eV, respectively, indicating the former has a stable structure than the latter. The band gaps of two systems are 3.1573 eV and 2.0155 eV, respectively, reveals that the band structures of them behave like semiconductors. The static dielectric constants of two systems are 40 and 37, respectively, which denotes their potential applications in electronics and optics. The strong absorption bands ranging from 4 eV to 16 eV become much sharper and show a red-shift after doping. The offset of 2Al-doped system is larger than that of 2Ca-doped system. The absorption coefficient can be remarkably modulated by doping. In calculated frequency-dependent electron energy loss spectra (EELS) of doping systems, the host peaks all locate at about 15 eV.

Ferroelectric and multiferroic materials form an important class of functional materials. Over the last 20 years, first-principles-based effective Hamiltonian approaches have been successfully developed to simulate these materials. In recent years, effective Hamiltonian approaches were combined with molecular dynamics (MD) methods to investigate terahertz dynamical properties of various perovskites. With this combination, a variety of ferroelectric and multiferroic materials, including BaTiO₃, Ba(Sr, Ti)O₃, Pb(Zr, Ti)O₃, BiFeO₃ and SrTiO₃ bulks and films have been simulated, which led to the understanding of complex phenomena and discovery of novel effects. In this paper we first provide technical details about effective Hamiltonians and MD simulation method. Then, we present applications of the combination of these two techniques to different perovskites. Finally, we briefly discuss possible future directions of this approach.

The structural, elastic and electronic properties of O-doped and un-doped cubic Zr₃N₄ and Ti₃N₄ are studied by first principles calculations based on the density functional theory. The bulk and shear moduli, as well as Young's moduli, decrease after doping with oxygen, which is due to the lengthening of the metal-nitrogen bond as well as the inflation of the cell volume. The changes in elastic properties are consistent with available experimental results. Both nitrides change from brittle to ductile when doped with oxygen, and all materials can be regarded as being elastic isotropic. The band structure and density of states are calculated to discuss the electronic properties of O-doped cubic Zr₃N₄ and Ti₃N₄, the presence of oxygen has significant influence on the electronic structure near the Fermi level. The gap at Fermi level is vanished which confirms the metallic character when O is introduced into nitrides. It means that doping with oxygen will have important effects on the optical properties of Zr and Ti nitrides.

Spontaneous polarization and its strain effects of bismuth titanate (BiT) with B2cb and B1a1 space groups are studied by first-principles density functional theory (DFT) calculation. B1a1 was proved to be the most stable phase structure and the spontaneous polarization is in good agreement with the experimental value. Similar variations of the principal polarization component (P_a) are obtained for B2cb and B1a1 structured BiT by applying b-uniaxial, c-uniaxial, ab-biaxial and bc-biaxial strains. It is found that the P_a is enhanced about 18.5% (20.8%) with ab-biaxial tensile strain of 2.4% for B2cb(B1a1) structure. Polarization along the c-axis (P_c) for the B1a1 structure is improved by 59.1% when bc-biaxial tensile strain reaches 2.4%.

We have studied the structural, electronic and dynamic properties of γ-Li₄SiO₄ (lithium orthosilicate) using density functional theory (DFT) with the generalized gradient approximation (GGA). The crystal structure is fully relaxed. The electronic band structure and Density of States (DOS) calculations indicate that γ-Li₄SiO₄ is an insulator with an indirect band gap of 5.19 eV and it has a conduction band with the width of 5.92 eV and two valance bands with the width of 4.45 eV and 0.57 eV, respectively. In the partial DOS, Li and Si electronic densities increase more sharply than O atoms. Comparing with previous works, the phonon dispersion curves without negative frequencies are calculated along high symmetry points. By adding the Born effective charges in the phonon calculation, the LO–TO splittings are also calculated which indicate that γ-Li₄SiO₄ is polar and anisotropic. The optical modes of phonon frequencies at Γ point are assigned as Raman and Infrared-active modes. Additionally, the thermodynamic functions (entropy, internal energy, Helmholtz free energies and constant-volume specific heats) were determined by using the phonon DOS. The calculated results may provide useful guidance of γ-Li₄SiO₄ for future experimental studies in some degree.

On the basis of first principles calculations, we have calculated the elastic properties, stress–strain relations, ideal tensile strengths, ideal shear strengths, and the ideal compressed strengths of Al and Al₃Mg. The stress–strain relations of Al₃Mg are strikingly similar to those of Al, indicating that the crystal structure appears to be more important than the identity of the individual atoms during uniaxial deformation. Al₃Mg is found to have larger moduli and higher strengths than Al but less ductile than Al. So Al₃Mg is expected to be a harder material, consistent with its exploitation in Al precipitate-hardening mechanisms. The calculated elastic properties, tensile strengths and shear strengths of Al are consistent with experimental values or previous theoretical results. We also use another method (molecular dynamics (MD) simulations) to recalculate elastic constants, ideal tensile and compressed strength of Al₃Mg for checking and comparing. We find that the results obtained by the two methods agree well with each other. The failure modes under uniaxial $〈100〉$ tension are also explored for Al and Al₃Mg. Our calculations confirm that Al fail by shear and predict that Al₃Mg also fail by shear.

Based on density functional theory (DFT) and local density approximation (LDA), the band structure and the density of states of all models of pure and V-doped anatase TiO₂ systems were calculated using plane-wave ultra-soft pseudo potential method after geometry optimization. The calculation results show that, with the increase of the doping concentration of V in anatase TiO₂, the free electron concentration and electron effective mass increase; the electronic mobility and electronic conductivity decrease, which is consistent with the change trend of the experimental results.

The structural, electronic and thermodynamic properties of cubic double perovskite Ba₂YTaO₆ are calculated by using the plane wave within density functional theory (DFT) framework employing the generalized gradient approximation (GGA). The ground state quantities including the lattice parameter, bulk moduli and its pressure derivative are fitted by the Birch–Murnaghan equation of state. The calculated energy band indicates that Ba₂YTaO₆ has a direct band gap of 3.42 eV at $G$ point in the Brillouin zone and the energy band near Fermi level is determined by the density of states of O 2$p$, Ta 5$d$ and Y 4$d$ electrons. The thermodynamic properties including Debye temperature, bulk moduli and heat capacity of various pressures and temperatures are calculated and analyzed. Results indicate that the temperature and induced pressure have significant effect on the thermodynamic properties of Ba₂YTaO₆.

The first-principle calculations have been performed to study the pressure-induced effects on the structural, electronic, elastic and lattice dynamical properties of defect chalcopyrite CdIn₂Te₄. The optimized structural parameters are well consistent with the available experimental and theoretical data. The evolutions of energy gaps, elastic constants, elastic moduli, phonon dispersion spectra, and Raman scattering spectra, as well as zone-center phonon frequencies with pressure have been investigated in detail. Our results show that CdIn₂Te₄ has a direct bandgap and energy gaps decrease nonlinearly with pressure. A pressure-induced transition from brittle fracture to plastic flow exists, and DC-CdIn₂Te₄ is elastic anisotropy. Most Raman-active phonon frequencies have positive pressure dependence, the exception is for the E² and B³ modes.

The structural, electronic, elastic and mechanical properties of ZrNiPb half-Heusler alloy under pressure ranging from 0 to 25 GPa have been studied using the density functional theory within the generalized gradient approximation (GGA). The results of ambient condition were in good agreement with the available theoretical and experimental data. Our electronic structure and density of state results show that ZrNiPb is an indirect bandgap semiconductor half-Heusler alloy with a narrow energy gap of 0.375 eV. Based on the calculated elastic constants (C${}_{11}$, C${}_{12}$ and C${}_{44}$), Young’s modulus (E), Poisson’s ratio ($\nu$), Shear modulus (G), Zener anisotropy factor (A) and brittle-ductile behaviors under pressure have been discussed. The calculated Poisson’s ratio shows that ZrNiPb undergoes a relatively small volume change during uniaxial deformation. We show that the chemical bonds in ZrNiPb are stronger due to the high value of C${}_{11}$.

A key property for the design of new shape memory alloys is their working temperature range that depends on their transformation temperature T₀. In previous works, T₀ was predicted using a simple linear regression with respect to the energy difference between the parent and the martensitic phases, $\mathrm{\Delta }$E${}_{p-m}$. In this paper, we developed an accurate method to predict T₀ based on machine learning assisted by the first-principles calculations. First-principles calculations were performed on 15 shape memory alloys; then, we proposed an artificial neural network method that used not only computed $\mathrm{\Delta }$E${}_{p-m}$ but also bulk moduli as input variables to predict T₀. The prediction error of T₀ was improved to 49 K for the proposed artificial neural network compared with 188 K for simple linear regression.

LAP crystal is an excellent nonlinear optical material and it has some unexplained specificities, which makes the interaction between groups in molecule received much attention. In this paper, the first-principles calculations are performed to investigate the intergroup interactions by the electronic structure and optical properties of LAP crystal. The energy gap of LAP crystal is 5.02 eV, indicating that the electronic transition is easier than KDP crystal. The strong electronic interaction between the carboxyl, phosphate and guanidine groups is found. In addition, since the LAP molecule has the greatest dipole in [010] direction and the electronic transitions are most likely to occur between the carboxyl group, phosphate and guanidine groups located on both ends of the molecule along [010] direction, the LAP crystal shows specific optical properties in this direction. The results reveal the correlations between the optical properties and the intergroup interactions of LAP crystal.

A complete theory is the guide and explanation of the experiment. According to the first principle, the stable structure of Ge vacancy color center (GeV) is the double vacancy center structure by using the constructed GeV color center supercell. The covalent radius and bond angle of GeV are explored by analyzing the microstructures. The electronic structure of GeV color center is calculated, and the charge transfers of GeV color center are explained, thereby demonstrating the existence of stable bonds. The principle of the energy-level transition of the GeV color center in terms of light emission is described. The effect of each element and energy level orbital is illustrated by the density-of-states diagram.

To analyze the contributions of the metal atoms to stabilize and synthesize the small cage-like carbon clusters, the configurations, electronic and magnetic characteristics of Mn-, Fe-, Co- and Ni-substituted C${}_{20}$ cage have been investigated using the PBE functional. The results demonstrate that the TM (TM=Mn, Fe, Co and Ni) substitution decreases the structural stability of the C${}_{20}$ cages, while increases the activity of the C${}_{20}$ cages. Electronic migrations between the TM atoms and C atoms are less. All the TM–C bonds of the TMC${}_{19}$ and TM₂C${}_{18}$ clusters display covalent bond characters. The $3s$ orbitals of TM atoms lose electrons, the $3d$ and $4p$ orbitals of TM atoms obtain electrons. The special distributions of the HOMO states of the TMC${}_{19}$ and TM₂C${}_{18}$ clusters are mainly from the hybridization of the C $p$ orbitals and the TM $d$ orbitals. The Mn₂C${}_{18}$ cages display the highest spin polarization.

First-principles calculations are performed to study the effects of defect on the structure and electronic properties of Ti₃SiC₂. The calculations show that the formation energy of Si vacancy is minimal compared with the Ti or C vacancies in Ti₃SiC₂. The defects of Si layer also can be formed under high-temperature or irradiation environments. The C-layers or Ti-layers are almost impossible to form. If the Si vacancy or Si layers are formed, they prefer to be substituted by the O and H atoms to form the MXene structure, and the unit cell of Ti₃SiC₂ lattice constant decreases in c-direction. However, it has quite slight effect on electronic properties of Ti₃SiC₂. The He impurities are almost impossible to occupy the Si vacancies, because the formation energy are 50.860 eV for one layer of Si atoms substituted by the He atoms. This type of defect leads to the lattice constant of Ti₃SiC₂ in c-direction increasing considerably. Therefore, Ti₃SiC₂ is a suitable candidate for nuclear materials because of the high-formation energies of He impurities under irradiation environment.

In this paper, electronic and optical properties of GaN/InN core/shell nanowires (CSNWs) have been theoretically investigated through the first principles calculations. The binding energy of In and N atoms on surface of six crystal planes along the $z$-axis of GaN nanowires are all negative, which indicate that In and N atoms can be effectively deposited on the surface of GaN nanowires and preparing GaN/InN CSNWs is feasible theoretically. Calculation results of electronic properties indicate that the core/shell ratio and diameter of GaN/InN CSNWs have significant effect on the band structure, bandgap can be effectively adjusted when keeping the number of GaN layers unchanged and changing the number of InN layers. Moreover, with the increase in the number of InN layers, the absorption spectrum of GaN/InN CSNW has significant redshift and few weak absorption peaks appear in the visible light region.