中文摘要：

运用第一性原理赝势方法，对氮化硅新相（六方P6和P6＇相）的电子结构、光学性质和相变过程进行分析，研究能带结构、介电函数谱、反射谱和能量损失函数的变化机理．研究发现，β→P6→δ相变是可行的，在室温下β→P6和P6→δ相变的临界压强分别为42．9和47．7GPa；相界的斜率为正值表明P6→δ相变过程伴随着晶胞体积的塌缩：P6和P6’相分别属于直接带隙和间接带隙半导体，能隙宽度分别为4．98和4．01eV；得到了两相的零频介电常数；反射谱表明，两相的强反射峰均位于真空紫外线区域，因此可以用作紫外光屏蔽或紫外探测材料；在可见光区域，两相表现为近似透明．

英文摘要：

Characteristics of the hexagonal polymorph Si3N4 i.e., phase transition, electronic and optical properties （band structure, dielectric function, reflectivity and energy loss function） are investigated by the first-principles pseudo-potential method. The results suggest that it is feasible that the β→P6→δ transition takes place at room temperature. The critical pressures of the β→P6 and P6→δ transformations are 42.9 and 47.7 GPa, respectively. The phase transition from P6→δ is accompanied by the volume shrinkage. The calculated results also show that the P6 and p6＇ phases belong to direct bandgap and indirect bandgap semiconductors, respectively. The calculated band gaps are 4.98 and 4.01 eV for the P6 and p6＇ phases, respectively. Besides, the static dielectric constants are also obtained. The reflectivity shows that the two phases can serve as the shielding and detecting devices for ultraviolet radiation and they have optical transparent behaviors in the visible light region.