高压下MgO的热弹性研究

利用第一原理平面波赝势方法和广义梯度近似研究了广泛温度和压强范围内MgO的热弹性特性．MgO从低压NaCl到高压CsCl结构的相变压强为397 GPa，表明它在地球内部不会发生相变．在压强上升到150 GPa时，MgO的绝热弹性模量跟0 GPa时的实验值和其他赝势在高压下的计算结果基本一致．从0 GPa上升到20 GPa时，MgO的各向异性逐渐减小；在20?150 GPa时绝对值逐渐增大．MgO明显地违背了Cauchy条件，反应出非中心多体力是重要的．另外，MgO的热力学参量与实验也符合的很好．

Thermoelasticity of MgO at High Pressures

The thermoelastic properties of MgO over a wide range of pressure and temperature are studied using the first-principles plane wave pseudopotential method within the generalized gradient approximation. It is shown that MgO remains in the B1 (NaCl) structure at all pressures existing within the Earth, and transforms into the CsCl-type structure at 397 GPa. The athermal elastic moduli of MgO are calculated, as a function of pressure up to 150 GPa. The calculated results are in excellent agreement with experimental data at zero pressure and compare favorably with other pseudopotential predictions over the pressure regime studied. MgO is found to be highly anisotropic in its elastic properties, with the magnitude of the anisotropy first decreasing between 0 and 20 GPa and then increasing from 20 GPa to 150 GPa. The Cauchy condition is found to be strongly violated in MgO, reflecting the importance of noncentral many-body forces. The thermodynamic properties of MgO are consistent with the experimental data at ambient condition.