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，了解其物理性质对阐明地球深部结构和化学特征具有重要意义。在这项研究中，采用精细的k点采样网格，对80个原子的超晶胞进行了恒温从头算分子动力学模拟，并对其数值精度进行了仔细的考察。结果表明，CaSiO_3钙钛矿的剪切模数最多降低39%，剪切速度最多降低22%。对典型地幔岩石的地震速度模拟结果表明，含有大量CaSiO_3钙钛矿的玄武岩的地震速度明显慢于以往的估计。这些结果表明，在下地幔观察到的弱S速度异常和S与块体速度的反相关关系等典型性质，可以由俯冲洋板产生的化学不均匀而不是由横向温度不均匀来协调。

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.