Sr偏析Al晶界结构的第一性原理计算

采用基于密度泛函理论和局域密度近似的第一性原理赝势方法,计算了纯Al晶界和杂质Sr偏析Al晶界的原子结构和电子结构.结果表明Sr偏析引起了晶界膨胀和晶界处电子密度的大幅度降低,从而导致晶界结合力的减弱.这应为Sr杂质偏析引起的Al晶界脆化的主要根源所在. 关键词： Al晶界 Sr 杂质偏析 第一性原理计算     

SrTiO3(001)表面上Au和N原子相互作用的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法研究了SrTiO₃(001)表面上Au和N原子间相互作用的微观机理.通过比较分析N置换表面层O原子前后SrTiO₃(001)表面吸附Au原子体系的相关能量和电子结构,发现SrTiO₃(001)表面吸附Au原子和N替代表面层O原子的置换过程二者之间存在明显的"协同效应",即N原子置换SrTiO₃(001)表面层O原子的过程增强了相应表面吸附Au原子的稳定性,而SrTiO关键词： 表面结构 相互作用 第一性原理     

Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co （200）： A first-principles density-functional study

First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co(200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co(200)substrate, which can gain a new insight into the growth mechanism of graphene.     

Influence of Ni and N on generalized stacking-fault energies in Fe-Cr-Ni alloy: A first principle study

The alloying effects of Ni and N were examined in terms of the generalized stacking-fault (SF) energy (GSFE). GSFE is associated with the basal plane of Fe-Cr-Ni austenitic stainless steel. The GSFE profiles were obtained using first-principle calculations. The results show that Ni increases the intrinsic SF energy γ_isf and the unstable SF energy γ_us. N does the opposite. However, a γ_isf/γ_us ratio close to zero accompanies the addition of Ni or N. This ratio implies that deformation by partial dislocation is preferred. Overall, the effect of N on Fe-Cr-Ni alloys is more evident than that of Ni.     

Effects of aluminum vacancies on electronic structure and optical properties of Ta4AlC3: A first principles study

We investigated the effect of aluminum vacancies (V_Al) on the structural, electronic and optical properties of Ta₄Al_1−xC₃ (x=0, 0.25, 0.5, 0.75) based on the first-principle calculation using density functional theory. We found that the lattice constant a remains almost unchanged with the variation of V_Al concentration, while c and c/a ratio decrease with increasing V_Al concentration. Moreover V_Al induced local distortions have significant influence on the electronic and optical properties of Ta₄AlC₃, especially beyond the critical V_Al concentration (x=0.5). On the other hand, the presence of V_Al can improve the dielectric properties of Ta₄AlC₃. From the optical properties analysis, we predicted that Ta₄Al_1−xC₃ is not suitable as a coating material to avoid solar heating.     

Effects of the structural order of canthaxanthin on the Raman scattering cross section in various solvents: A study by Raman spectroscopy and ab initio calculation

In this work,we measure the Raman scattering cross sections(RSCSs) of the carbon-carbon(CC) stretching vibrational modes of canthaxanthin in benzene,acetone,n-heptane,cyclohexane,and m-xylene.It is found that the absolute RSCS of CC stretching mode of canthaxanthin reaches a value of 10 24 cm 2 ·molecule 1 ·sr 1 at 8×10 5 M,which is 6 orders of magnitude larger than general RSCS(10 30 cm 2 ·molecule 1 ·sr 1),and the RSCSs of canthaxanthin in various solvents are very different due to the hydrogen bond.A theoretical interpretation of the magnetic experimental results is given,which is introduced in a qualitative nonlinear model of coherent weakly damped electron-lattice vibration in the structural order of polyene chains.In addition,the optimal structure and the bond length alternation(BLA) parameter of canthaxanthin are calculated using quantum chemistry calculation(at the b3lyp/6-31g(d,p) level of theory).The theoretical calculations are in good agreement with the experimental results.Furthermore,the combination of Raman spectroscopy and the quantum chemistry calculation study would be a quite suitable method of studying the structures and the properties of the π-conjugated systems.