Structure evolution and transport properties of CaSiO_{3} melt under mantle conditions from deep potential...

Silicate melts play a crucial role in shaping Earth's geological features and influencing various geophysical phenomena. Transport properties of silicate melts control magma ocean dynamics on the early terrestrial planets and affect the chemical structure of Earth's deep interior. Here we have developed a deep-learning potential to investigate the structural evolution and transport properties of CaSiO_{3} melt, a major component of basaltic magmas that is expected to exist in Earth's lower mantle. Our findings reveal that, with increasing compression, the average Si-O coordination number shows a nearly linear increase from fourfold at ambient pressure to sixfold in the lower mantle, with fivefold coordination serving as a transition state. The Ca-O coordination trend under compression parallels that of Si-O, except that sixfold coordination dominates at ambient pressure, while ninefold prevails at lower mantle pressure. At high pressures, the temporal evolution of cation-oxygen bonding exhibits frequent bond-breaking events. Meanwhile, the quantified lifetimes of different cation-oxygen species show that Ca species act as network modifiers, whereas Si species function as network formers. The calculated diffusion coefficients align favorably with available first-principles data, except in the supercooled state transition region. Between 2500 and 5000 K, viscosity increases with pressure, which can be attributed to enhanced structural polymerization due to the increased abundance of highly coordinated cation species. These insights into the CaSiO_{3} melt could provide a fundamental basis for understanding the dynamics of magma ocean evolution.