Abstract
Ultrahigh-pressure phase boundary between solid and liquid SiO2 is still quite unclear. Here we present predictions of silica melting curve for the multimegabar pressure regime, as obtained from first principles molecular dynamics simulations. We calculate the melting temperatures from three high pressure phases of silica (pyrite-, cotunnite-, and Fe2P-type SiO2) at different pressures using the Z method. The computed melting curve is found to rise abruptly around 330 GPa, an increase not previously reported by any melting simulations. This is in close agreement with recent experiments reporting the α-PbO2–pyrite transition around this pressure. The predicted phase diagram indicates that silica could be one of the dominant components of the rocky cores of gas giants, as it remains solid at the core of our Solar System’s gas giants. These results are also relevant to model the interior structure and evolution of massive super-Earths.
Highlights
Planets appear to be far more diverse than previously thought, and knowledge of the mineralogy of super-Earth planets is essential for understanding their interior structure, thermal behavior, and long-term evolution
Material properties, which can be calculated from electronic structure theory or measured experimentally on Earth, and it is an essential component of interior structure models for exoplanets
While free SiO2 is only housed in localized regions of the Earth’s mantle, such as subducted oceanic crust, the higher P-T conditions and expanded range of plausible compositions in super-Earth exoplanets allow for greater possible presence of silica phases in terrestrial exoplanets, forming the bulk composition of super-Earths[5,9,18,19] as well as the rock-ice protocores that result in gas giants through core accretion[20]
Summary
Planets appear to be far more diverse than previously thought, and knowledge of the mineralogy of super-Earth planets is essential for understanding their interior structure, thermal behavior, and long-term evolution. Giant planets resemble natural laboratories for studying the behavior of materials at high pressure and temperature, which typically reach values outside the realm of experiment Theoretical approaches, such as ab initio simulations, provide the best available guide to study the properties of matter at such extreme conditions[1,14,15]. It has been determined that MgSiO3 dissociates in the cores of gas giants and terrestrial exoplanets[21,22], leaving SiO2 and MgO as important separate compounds that form the rocky interior of these planets In this context, the phase diagram of silica becomes fundamental. The solid-liquid boundary for silica at higher pressures remains unknown
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