压力下钒发生相变的第一性原理计算

First principles calculation of phase transition of vanadium under pressure

利用投影缀加波方法对金属钒加压至400GPa左右的结构相变过程进行了第一性原理研究.计算了相变中的热力学转变压力和失稳转变压力,并对相变前后的电子性质进行了研究.结果表明:钒在低压下为体心立方结构,随着压力增大转变为菱方结构,压力继续增大最后又重新转变为体心立方结构.热力学计算得到的BCC→rhu(α>109.47°)→rhl(α<109.47°)→BCC三次转变压力分别为27,104和310GPa.利用剪切弹性常数C44计算得到的2次失稳压力分别为52和255GPa.能带计算表明,在加压过程中高对称点Γ处靠近费米能级的能带由低压下的非电子占据态变为高压下的占据态,而费米能级以上的电子态密度计算可见明显的s,p-d带间电子迁移现象.

Recent experiment revealed a new structural phase transition in vanadium at high pressure. Here the whole phase transition process under pressure up to 400 GPa was investigated from first principles calculation with projector augmented wave （PAW） method. The results show that body - centered cubic （BCC） vanadium firstly makes a transition to rhombohedral（rh） structure under pres- sure, and with increasing pressure, it transforms back to BCC again. Three thermodynamic phase transition pressures of BCC→rh^u （ α 〉 109.47°） →rh^1 （ α 〈 109.47°） →BCC are 27, 104 and 310 GPa, respectively. Two instability pressures obtained by calculation of shear elastic constant C44 at different pressures are 52 and 255 GPa. Electronic properties calculation reveals that bands near F point gradually move below the Fermi level and become occupied condition. Calculation of decomposed density of states at Fermi level presents obvious s,p-d electrons transition among bands.