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四方和正交以及单斜相K0.5Na0.5NbO3的结构稳定性和电子结构的第一性原理研究*
First-principles study of structural stability and electronic properties of tetragonal and orthorhombic as well as monoclinic K0.5Na0.5NbO*3
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摘要: 采用基于密度泛函理论框架下的第一性原理超原胞方法和虚晶近似方法，在局域密度近似和广义梯度近似下，对四方和正交以及单斜相K0.5Na0.5NbO3的能量和原子结构以及电子结构进行了系统的研究.计算结果表明三种K0.5Na0.5NbO3相的能量差别较小，这与实验上它们之间容易发生相转化是一致的.进一步发现单斜相的能量比四方相和正交相低，说明单斜相结构更加稳定，并且理论计算的结构参数与实验值符合得很好.电子结构结果也表明单斜相的键合作用比四方相和正交相键合作用更强，进一步说明单斜相结构更加稳定.Abstract: The energetic stability, structural and electronic properties of tetragonal, orthorhombic, as well as monoclinic K0.5Na0.5NbO3 are systematically studied using first-principles supercell model and virtual crystal approximation based on density functional theory with local density approximation and generalized gradient approximation. Our calculated results show that the total energy differences among the three K0.5Na0.5NbO3 phases are small, which are well consistent with the easy phase equilibrium at the phase boundary in the experiments. Furthermore, we also find that the total energy of the monoclinic phase is lower than that of the other two phases, which suggests that the monoclinic structure is energetically more stable than the others. Moreover, the calculated structural parameters are in good agreement with experimental values. In addition, the electronic structure results show that the bonding interaction in the monoclinic structure is stronger than that in the other structures, also indicating that the monoclinic structure is the most stable one.
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