Ab initio investigations on the high-pressure and temperature elasticity of calcium silicate perovskite

CaSiO_3钙钛矿是主要的下地幔组成矿物之一，了解其物理性质对详细阐明地球深部结构和化学具有重要意义。在本研究中，采用精细k点采样网格，对80个原子的超级单体进行了恒温从头算分子动力学模拟，并注意数值精度。结果表明，CaSiO_3钙钛矿的剪切模量最多比前人报道的小39%，剪切速度最多慢22%。模拟的典型地幔岩石地震速度表明，含较多CaSiO_3钙钛矿的玄武岩的地震速度比以往的估计要慢得多。结果表明，下地幔的典型特征，如弱S速度异常和S速度与体速度的反相关，可以由俯冲洋板块产生的化学非均质性来调和，而不是由横向温度非均质性来调和。

CaSiO_3 perovskite is one of major lower mantle constituent minerals, and it is important to understand its physical properties to clarify the Earth's deep structure and chemistry in detail. In this study, constant-temperature ab initio molecular dynamics simulations were performed with careful attention to the numerical accuracy for an 80-atoms supercell with applying a fine k-points sampling mesh. Results clarified that CaSiO_3 perovskite has at most 39% smaller in shear modulus, and thus at most 22% slower in shear velocity, than those reported in previous studies. Seismic velocities of typical mantle rocks modeled based on the obtained results indicated that the basaltic rock containing many CaSiO_3 perovskite has the velocity substantially slower than previous estimations. It was found from these results that typical properties observed in the lower mantle such as the weak S-velocity anomaly and the anticorrelation between S and bulk velocities can be reconciled by chemical heterogeneity produced by subducted oceanic slabs not by lateral temperature heterogeneity.