The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.
The US President Obama launched the Materials Genome Initiative on June 24,2011,aimed at speeding up the pace of discovering,developing,manufacturing,and deploying advanced materials by at least twice as fast as is possible at present,at a fraction of the cost with the help of existing advanced computer technology.According to the authors’understanding to the event,this article will first give a brief discussion on the origin of material genome,its scientific implication,research significance,and the far-reaching influence of materials genome study to the developments of materials science and human society.Then,the subsequent contents will introduce the research progresses of the related works carried out by the authors’research group over the last decade,on the first-principles studies of crystalline materials genome.The highlights are focused on the method implementations for configuration optimization of lattice structure,first-principles calculations of various physical parameters on elastic,electronic,dielectric,and thermodynamic properties,and simulations of phase transition and particle transport in solids.The technical details for extending these methods to low-dimensional crystalline materials are also discussed.The article concludes with an outlook on the prospect of materials genome research.
镁合金长周期堆垛有序相(Long Period Stacking Ordered,LPSO)微观结构的清晰描述对镁合金LPSO相形成及强化机制的研究具有十分重要的意义。借助第一原理计算及高分辨成像模拟研究,我们得到了难以通过实验方法获得的关于镁合金LPSO相原子尺度微观结构的清晰描述。研究发现,Zn、Y合金元素在LPSO相中易于形成多种ZnmYn(Mg)团簇。基于Zn6Y8(Mg)团簇,我们构建了14H相晶体学模型Mg142Zn12Y16,其高分辨模拟像几乎再现了高分辨实验像。基于该模型,我们计算确定了14H相的热力学稳定性、弹性常数及弹性模量。此外,基于Mg-Zn-Y合金LPSO相的计算研究,我们推断X6Z8(Mg)团簇可看作镁合金Mg-X-Z中LPSO相形成的"特征结构单元",理论上可基于该"结构单元"构建相应镁合金LPSO相模型并通过计算方法判别该合金中LPSO相形成的可能性(X、Z为任一合金化元素)。
First principle computational tensile tests （FPCTT） are performed to the Al ∑5 grain boundaries （GBs） with and without substitution or interstitial Si impurity. The obtained stress-strain relationships and atomic configurations demonstrate that the Al ∑5 GBs with and without substitutional or interstitial Si impurity show different fracture modes. The mechanisms of the different fracture modes are analyzed based on the charge density and the density of states. The results show that the charge redistributions of the atoms in the vicinity of GBs and the covalent interactions between Si and its neighboring Al atoms determine the fracture modes.
