中文摘要：

数值计算了四方、单斜和正交结构Ge_3N_4的点阵常数、晶胞体积、弹性模量、维氏硬度和态密度.计算结果与已有的实验数据和理论值符合得很好.形成焓为负、晶格形变和晶胞体积随压强呈线性变化,表明三种相在0～20 GPa压强范围内可以保持结构稳定.态密度研究表明三种氮化锗内部存在强烈的s-p杂化.三种相都属于脆性半导体材料,具备各向异性且硬度适中.采用包含原子振动和非谐效应的准谐波近似方案,研究材料的热力学性质,发现压强对赫姆霍兹自由能和内能有显著影响.结果为进一步理解氮化锗三种新结构的电子结构和热力学性质提供初步的物理图像.

英文摘要：

We calcuate lattice constants, volumes, elastic moduli, Vickers hardnesses and density of states of the tetragonal, monoclinic and orthorhombic Ge3N4. Fundamental properties obtained are compared with experimental data and other theoretical results, which shows good agreement. Negative formation enthalpy, linear relation between lattice deformation and pressure, and volume show that three phases retain stabilities in a pressure range of 0 - 20 GPa. Density of states show that G% N4 are semiconductors with strong s-p hybridizations. All polymorphs are brittle materials but anisotropic. Several thermodynamic properties are investigated with quasi-harmonic approach considering lattice vibrations and anharmonic effects. Helmholz free energy and internal energy show strong dependences on pressure. Interesting features are seen in heat capacity of the novel Ge3N4 nitrides, especially at high temperatures.