Ga、N、P、Sb掺杂二维砷烯吸附SO2气体的第一性原理研究

基于第一性原理计算，研究了Ga、N、P、Sb元素分别掺杂本征砷烯材料对SO2气体的吸附特性。结果表明，Ga掺杂的砷烯表现为直接带隙半导体；本征砷烯以及P、Sb掺杂的砷烯对SO2呈较弱的物理吸附，N掺杂的砷烯在4种体系中展现出最大的吸附能，为-0.867 eV，不利于SO2解吸；Ga掺杂的砷烯对SO2具有适中的吸附能，为-0.693 eV，同时，吸附SO2前后带隙值变化最显著（0.957 eV），有望作为高效检测SO2的气敏材料。     

Cobalt-based coordination polymer as high activity electrocatalyst for oxygen reduction reaction: Catalysis by novel active site CoO4N2

[{Co₃(μ₃-OH)(BTB)₂(BPE)₂}{Co_0.5N(C₅H₅)}] (Co-CP) as a coordination polymer for catalyzing oxygen reduction reaction (ORR) has recently been reported to exhibit high ORR performance because of its novel structural characteristics. Nevertheless, the detailed mechanism remains far from enough. Herein, first-principles study of the ORR process of Co(C₆H₅CO₂)₂(C₅H₅N)₂ is carried out, which is the constructed model of monomeric unit for this compound. Most interestingly, the calculated results uncover that in the second proton transfer step, the active site contributes to the reaction is not only the Co atom, but also the O and N atoms which are directly bonded to the Co atom that construct a novel active site CoO₄N₂. Further analysis of the electronic structure demonstrates that the Co, O, and N atoms in the CoO₄N₂ local structure have participated the electron transfer during the entire ORR process. By analyzing the relative energy changes of whole reaction, it can find that the favorable ORR pathway on the Co(C₆H₅CO₂)₂(C₅H₅N)₂ is the 4e⁻ pathway, and the overpotential of ORR on Co(C₆H₅CO₂)₂(C₅H₅N)₂ is calculated as 0.43 V, which is consistent with experimental observation and lower than that on the Pt(111). Furthermore, the results of first-principles molecular dynamics simulations and density of states (DOS) show that Co(C₆H₅CO₂)₂(C₅H₅N)₂ presents good stability. And it also possesses high anti-poisoning ability to some impurity gases such as CO, NO, and NH₃.     

An integrated framework for multi-scale materials simulation and design

In this paper, we describe initial results of an ongoing research activity involving materials scientists, computer scientists, mathematicians, and physicists from academia, industry and a national laboratory. The present work aims to develop a set of integrated computational tools to predict the relationships among chemistry, microstructure and mechanical properties of multicomponent materials systems. It contains a prototype grid-enabled package for multicomponent materials design with efficient information exchange between structure scales and effective algorithms and parallel computing schemes within individual simulation/modeling stages. As part of our multicomponent materials design framework, this paper reports the materials simulation segment in developing materials design knowledgebase, which involves four major computational steps: (1) Atomic-scale first-principles calculations to predict thermodynamic properties, lattice parameters, and kinetic data of unary, binary and ternary compounds and solutions phases; (2) CALPHAD data optimization approach to compute thermodynamic properties, lattice parameters, and kinetic data of multicomponent systems; (3) Multicomponent phase-field approach to predict the evolution of microstructures in one to three dimensions (1–3D); and (4) Finite element analysis to generate the mechanical response from the simulated microstructure. These four stages are to be integrated with advanced discretization and parallel algorithms and a software architecture for distributed computing systems.     

An accurate theoretical study on intrinsic defect energetics in rutile TiO2

An accurate theoretical study on the intrinsic point defects in rutile TiO2 was carried out by first-principles calculations using plane-wave pseudopotential method. The structural parameters of defect-free bulk rutile TiO2 were calculated, which are close to experimental data. And the effects of point defects on the geometry structures were analyzed. To get accurate value of formation energy and charge transfer levels, several technical details must be considered, such as the position of EvBM originating from supercell size and electrostatic interactions between the charged defects, and band-gap error etc. The formation energies of the point defects in various charge states were given as a function of Fermi level for the two limiting values of extreme O-rich conditions and extreme Ti-rich conditions. Under extreme Ti-rich conditions, Ti^4＋ interstitial and Vo^2＋ have very low formation energy, and wound thus exist in significant quantities, namely, producing the intrinsic n-type TiO2. The stability of these point defects is traced back to the multivalence of titanium. Under extreme reducing condition, Frenkel defect comprised of Tii^4＋ and VTi^＋4 would be formed in TiO2.     

First-principles study of the growth and diffusion of B and N atoms on the sapphire surface with h-BN as the buffer layer

Currently,the preparation of large-size and high-quality hexagonal boron nitride is still an urgent problem.In this study,we investigated the growth and diffusion of boron and nitrogen atoms on the sapphire/h-BN buffer layer by first-prin-ciples calculations based on density functional theory.The surface of the single buffer layer provides several metastable adsorp-tion sites for free B and N atoms due to exothermic reaction.The adsorption sites at the ideal growth point for B atoms have the lowest adsorption energy,but the N atoms are easily trapped by the N atoms on the surface to form N-N bonds.With the in-creasing buffer layers,the adsorption process of free atoms on the surface changes from exothermic to endothermic.The diffu-sion rate of B atoms is much higher than that of the N atoms thus the B atoms play a major role in the formation of B-N bonds.The introduction of buffer layers can effectively shield the negative effect of sapphire on the formation of B-N bonds.This makes the crystal growth on the buffer layer tends to two-dimensional growth,beneficial to the uniform distribution of B and N atoms.These findings provide an effective reference for the h-BN growth.     

First-principles exploration of defect-pairs in GaN

Using first-principles calculations,we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair.15 defect-pairs with short defect–defect distances are found to be stable during structural relaxation,so they can exist in the GaN lattice once formed during the irradiation of high-energy particles.9 defect-pairs have formation energies lower than 10 eV in the neutral state.The vacancy-pair VN–VN is found to have very low formation energies,as low as 0 eV in p-type and Ga-rich GaN,and act as efficient donors producing two deep donor levels,which can limit the p-type doping and minority carrier lifetime in GaN.VN–VN has been overlooked in the previous study of defects in GaN.Most of these defect-pairs act as donors and produce a large number of defect levels in the band gap.Their formation energies and concentrations are sensitive to the chemical potentials of Ga and N,so their influences on the electrical and optical properties of Ga-rich and N-rich GaN after irradiation should differ significantly.These results about the defect-pairs provide fundamental data for understanding the radiation damage mechanism in GaN and simulating the defect formation and diffusion behavior under irradiation.     

Effect of lanthanum on the precipitation of NbC in bcc Fe

The effect of lanthanum on the precipitation of NbC in bcc Fe has been investigated by the first-principles calculations in combination with the experiments. The interactions of La–C are repulsive in the first-, second- and third-nearest-neighbour configurations, and the binding energies of La with Nb were predicted to be positive, and converge to a weak value. The addition of La decreases the solubility of C (above 763?K) and Nb, and increases the chemical potential of these two solutes, thus promoting the precipitation of NbC in bcc Fe. The experimental results show that the La-contained Nb-bearing steel has a relatively faster precipitation rate of NbC than the La-free steel, during isothermal treatment in ferritic region.     

Methylammonium cation deficient surface for enhanced binding stability at TiO<Subscript>2</Subscript>/CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> interface

Heterojunction interfaces in perovskite solar cells play an important role in enhancing their photoelectric properties and stability.Till date,the precise lattice arrangement at TiO2/CH3NH3PbI3 heterojunction interfaces has not been investigated clearly.Here,we examined a TiO2/CH3NH3PbI3 interface and found that a heavy atomic layer exists in such interfaces,which is attributed to the vacancies of methylammonium (MA) cation groups.Further,first-principles calculation results suggested that an MA cation-deficient surface structure is beneficial for a strong heterogeneous binding between TiO2 and CH3NH3PbI3 to enhance the interface stability.Our research is helpful for further understanding the detailed interface atom arrangements and provides references for interfacial modification in perovskite solar cells.     

Comparative research on the influence of varied Al component on the active layer of AlGaN photocathode

To theoretically research the influence of a varied Al component on the active layer of AlGaN photocathodes, the first principle based on density functional theory is used to calculate the formation energy and band structure of Al_xGa_1-xN with x at 0, 0.125, 0.25, 0.325, and 0.5. The calculation results show that the formation energy declines along with the Al component rise, while the band gap is increasing with Al component increasing. Al_xGa_1-x with x at 0, 0.125, 0.25, 0.325, and 0.5 are direct band gap semiconductors, and their absorption coefficient curves have the same variation tendency. For further study, we designed two kinds of reflection-mode AlGaN photocathode samples. Sample 1 has an Al_xGa_1-x active layer with varied Al component ranging from 0.5 to 0 and decreasing from the bulk to the surface, while sample 2 has an Al_xGa_1-x active layer with the fixed Al component of 0.25. Using the multi-information measurement system, we measured the spectral response of the activated samples at room temperature. Their photocathode parameters were obtained by fitting quantum efficiency curves. Results show that sample 1 has a better spectral response than sample 2 at the range of short-wavelength. This work provides a reference for the structure design of the AlGaN photocathode.     

Lithium intercalation mechanism for β-SnSb in Sn-Sb thin films

Based on the first-principles plane wave pseudo-potential method, the electronic structure and electrochemical performance of LixSn4Sb4 (x=2, 4, 6, and 8) and LixSn12-xSb4 (x=9, 10, 11, and 12) phases were calculated. A Sn-Sb thin film on a Cu foil was also prepared by radio frequency magnetron sputtering. The surface morphology, composition, and lithium intercalation/extraction behavior of the fabricated film were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic volta...