压强下TaB和TaB2力学和超导性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法, 在广义梯度近似下研究了TaB和TaB2在不同压强下的弹性常数、原子结构、电子结构以及超导性质及其对两者物理性质不同进行了比较. 计算结果表明随着压强的增加, 弹性常数和体弹模量随之增加, 而相对晶格常数a/a0, b/b0, c/c0和相对体积V/V0随压强增加而减小. 在高压下, TaB沿着a轴方向的压缩性要比b轴方向大, 而b轴方向的压缩性要比c轴方向大; TaB2是沿着c轴方向的压缩性要比a轴方向的压缩性大. 电子结构分析表明TaB2的原子态杂化程度比TaB的原子态杂化程度要高, 这与TaB2的体弹模量比TaB的体弹模量高的结果相一致. 依据Bardeen-Cooper-Schrieffer超导理论, TaB和TaB2费米能级处态密度的值随着压强的增加而降低, 说明它们的超导转变温度Tc随着压强的增加而降低.

First-principles study on mechanical and superconducting properties of TaB and TaB2 under pressure

The elastic constants, structural parameters, electronic structures and superconducting properties of TaB and TaB2 under pressure are investigated using first-principles based on plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA) and those different physical properties of them are analyzed. It is found that the elastic constants and bulk modulus of TaB and TaB2 increase with pressure, while variations of ratios a/a0, b/b0, c/c0 and normalized volume V/V0 decrease with pressure. Under high pressure, the a-axis of TaB is more compressible than the b-axis and the b-axis more than the c-axis, while the c-axis of TaB2 is more compressible than the a-axis of TaB2. Electronic structure analysis shows that the hybridization of atomic states of TaB2 is higher than that of TaB, which is in agreement with the result that the bulk modulus of TaB2 is higher than that of TaB. According to Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, values of DOS at Fermi levels of TaB and TaB2 decrease with pressure, respectively, which indicates that their superconducting transition temperatures Tc decrease as pressure increases.