中文摘要：

运用基因遗传算法的晶格结构预测技术预测Pd基Heusler合金Pd 2 MnSn、Pd 2 CrGa和Pd 2 FeGa的结构；采用基于密度泛函理论（DFT）的投影缀加波（PAW）方法研究Pd 2 CrGa和Pd 2 FeGa的四方变形、磁性、态密度、弹性常数和声子谱线，最后通过Helmholtz自由能的计算预测了Pd 2 CrGa和Pd 2 FeGa的相变温度。结构预测显示：极限条件0 K时，Pd2MnSn以L21立方结构稳定存在，而Pd2CrGa和Pd2FeGa均以四方结构稳定存在。四方变形中，Pd2CrGa、Pd 2 FeGa在c/a＜1.0和c/a＞1.0处均有一个能量的局域最小值，分别对应一个稳定的结构。Pd 2 CrGa、Pd 2 FeGa在两种状态下均表现为铁磁性，Cr原子和Fe原子是总磁矩的主要贡献者。弹性常数计算结果显示：Pd 2 CrGa和Pd 2 FeGa仅在四方结构时才满足稳定性判据。c/a≈1.24处的四方结构Pd2CrGa转变为立方结构的相变温度在350 K左右， c/a≈1.30处的四方结构Pd2FeGa转变为立方结构的相变温度在130 K左右。

英文摘要：

Based on genetic algorithm, the structures of Pd-based Heusler alloy Pd2MnSn, Pd2CrGa and Pd2FeGa were forecasted. The tetragonal distortion, magnetic, DOS elastic constants and phonon dispersion spectra of Pd2CrGa and Pd2FeGa were calculated by first-principles calculation based on DFT with projector augmented wave pseudopotential （PAW）. At last, based on the result of Helmholtz free-energy, the phase transition temperatures of Pd2CrGa and Pd2FeGa were predicted. The crystal structure prediction shows that Pd2MnSn is L21 cubic structure, but Pd2CrGa and Pd2FeGa are tetragonal structures at 0 K. The tetragonal distortion analysis show that there are local minimums total energy atc/a＆lt;1.0 andc/a〉1.0, which correspond to stable martensitic phases. Pd2MGa （M=Cr,Fe） are ferromagnetic in these two postures, and M （M=Cr,Fe） is the main magnetic contribution to its alloys, respectively. The elastic constants of Pd2CrGa, Pd2FeGa show that, cubic structure doesn’t satisfy stability conditions, but tetragonal structure satisfy the stability conditions atc/a≈1.24 andc/a≈1.30, respectively. Based on the results of Helmholtz free-energy, the phase transition temperatures of Pd2CrGa and Pd2FeGa tetragonal structure transferring to cubic structure are about 350 K and 130 K, respectively.