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

CaSiO_3钙钛矿是下地幔的主要组成矿物之一，了解其物理性质对详细阐明地球深部结构和化学性质具有重要意义。在这项研究中，恒温从头计算分子动力学模拟进行了仔细的注意，一个80个原子的超原胞的数值精度与应用精细的k点采样网格。结果表明，钙钛矿型CaSiO_3的剪切模量最多比前人报道的小39%，剪切速度最多比前人报道的慢22%。对典型地幔岩石的地震波速度进行了模拟，结果表明，含有大量CaSiO_3钙钛矿的玄武质岩石的地震波速度明显低于前人的估计。从这些结果中发现，在下地幔中观察到的典型性质，如弱的S-速度异常和S和体速度之间的关系可以通过俯冲洋板块产生的化学不均匀性而不是横向温度不均匀性来协调。

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.