论文部分内容阅读
后钙钛矿MgSiO3对于重新认识地球的基本结构和成分具有重大意义.采用基于密度泛函理论的第一性原理计算对后钙钛矿MgSiO3在静水压力和单轴压力下的弹性性质和地震波速特征进行了研究.首先通过总能比较和力学稳定性判据验证了后钙钛矿MgSiO3在高压下的稳定性,并且计算得到的晶格常数与前人结果符合很好.计算表明在高压下(D层),后钙钛矿具有比钙钛矿大的体变模量、剪切模量及密度,并且具有大的地震波速,这与地震观测D层中地震波速的不连续性一致.在静水压力作用下,计算结果显示压缩波各向异性基本保持不变,而剪切波各向异性增强.有单轴应力作用时,后钙钛矿地震波各向异性差异非常明显,当压力作用在a轴或c轴上时,能够得到比对应静水压力下后钙钛矿更强的各向异性,而恰好相反的是,压缩b轴时,各向异性有减小的趋势.本研究能为解释地幔底部地震波不连续性和横向差异提供一定的参考.
The post-perovskite MgSiO3 is of great significance for the re-understanding of the Earth’s basic structure and composition.First-principles calculations based on the density functional theory are used to calculate the elastic properties and seismic velocities of post-perovskite MgSiO3 under hydrostatic pressure and uniaxial pressure The stability of post-perovskite MgSiO3 under high pressure is verified by the comparison of the total energy and the criterion of mechanical stability, and the calculated lattice constants are in good agreement with the previous results.The calculated results show that under high pressure (D layer), the post-perovskite has larger bulk modulus, shear modulus and density than the perovskite and has a large seismic velocity, which is not related to the seismic velocity The continuity is consistent.According to the hydrostatic pressure, the calculated results show that the compressional anisotropy of the compressive wave basically remains unchanged and the anisotropy of the shear wave increases.When the uniaxial stress is acting, the anisotropy of post-perovskite seismic wave is very obvious , When the pressure acts on the a-axis or the c-axis, a stronger anisotropy can be obtained than after the corresponding hydrostatic pressure, while on the contrary the anisotropy tends to decrease as the b-axis is compressed This study can be interpreted Provide a reference for the discontinuity and lateral difference of seismic wave at the bottom of mantle.