A new direct band gap silicon allotropeο-Si32

Silicon is a preferred material in solar cells,and most of silicon allotropes have an indirect band gap.Therefore,it is important to find new direct band gap silicon.In the present work,a new direct band gap silicon allotrope of o-Si32 is discovered.The elastic constants,elastic anisotropy,phonon spectra,and electronic structure of o-Si32 are obtained using first-principles calculations.The results show that o-Si32 is mechanically and dynamically stable and is a direct semiconductor material with a band gap of 1.261 e V.     

液态Mg7Zn3合金快速凝固过程中微观结构演变机理的模拟研究

采用分子动力学方法对液态Mg₇Zn₃合金的快速凝固过程进行了模拟研究,并采用双体分布函数、Honeycutt-Andersen键型指数法、原子团类型指数法(CTIM)以及遗传跟踪等方法对凝固过程中团簇结构的形成、演变特性进行了分析.结果表明:在以冷速为1×10¹² K ·s^-1的凝固过程中, Zn-Zn原子之间的相互成键的概率明显增加,形成以1551,1541,1431键型为主的非晶态结构.其特征键型1551随温度变化 关键词： 液态MgZn合金 快速凝固过程 微观结构演变 分子动力学模拟     

A new direct band gap silicon allotrope o-Si32

Silicon is a preferred material in solar cells, and most of silicon allotropes have an indirect band gap. Therefore, it is important to find new direct band gap silicon. In the present work, a new direct band gap silicon allotrope of o-Si32 is discovered. The elastic constants, elastic anisotropy, phonon spectra, and electronic structure of o-Si32 are obtained using first-principles calculations. The results show that o-Si32 is mechanically and dynamically stable and is a direct semiconductor material with a band gap of 1.261 eV.     

Stability,elastic anisotropy,and electronic properties of Ca_2C_3

The systematic investigations of the mechanical, elastic, and electronic properties, and stability of the newly synthesized monoclinic C2/m-Ca_2C_3 are performed, based on the first-principles calculations. Ca_2C_3 is found to be mechanically and dynamically stable only from 0 GPa to 24 GPa. The elastic anisotropy studies show that Ca_2C_3 exhibits the elastic anisotropy increasing with the augment of pressure. Furthermore, using the HSE06 hybrid functional, the electronic properties of Ca_2C_3 under pressure are calculated. The structure can be regarded as a quasi-direct band gap semiconductor, and the pressure-induced direct-indirect band gap transition is studied in detail.