Novel high-pressure calcium carbonates

The exceptional ability of carbon to form sp2 and sp3 bonding states leads to a great structural and chemical diversity of carbon-bearing phases at non-ambient conditions. Here we use laser-heated diamond anvil cells combined with synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations to explore phase transitions in CaCO3 at P > 40 GPa. We find that post-aragonite CaCO3 transforms to the previously predicted P21/c-CaCO3 with sp3-hybridized carbon...

The behaviour of alkaline carbonates at high pressure is poorly understood. Indeed, theoretical and experimental investigations of general trends of pressure induced structural changes appear in the literature only sporadically. In this article we use a combination of ab-initio calculations and high-pressure experiments in diamond anvil cell to determine crystal structures of high-pressure phases of K2CO3. The comparison with experimental data on Li2CO3 allows to reconstruct ...

Investigating the fate of dissolved carbon dioxide under extreme conditions is critical to understanding the deep carbon cycle in the Earth, a process that ultimately influences global climate change. We used first-principles molecular dynamics simulations to study carbonates and carbon dioxide dissolved in water at pressures (P) and temperatures (T) approximating the conditions of the Earth's upper mantle. Contrary to popular geochemical models assuming that molecular CO$_2$...

Using ab initio evolutionary simulations, we explore all the possible stoichiometries for Mg-O system at pressures up to 850 GPa. In addition to MgO, our calculations find that two extraordinary compounds MgO2 and Mg3O2 become thermodynamically stable at 116 GPa and 500 GPa, respectively. Detailed chemical bonding analysis shows large charge transfer in all magnesium oxides. MgO2 contains peroxide ions [O-O]2-, while non-nuclear electron density maxima play the role of anions...

Experimental studies established that calcium undergoes several counterintuitive transitions under pressure: fcc \rightarrow bcc \rightarrow simple cubic \rightarrow Ca-IV \rightarrow Ca-V, and becomes a good superconductor in the simple cubic and higher-pressure phases. Here, using ab initio evolutionary simulations, we explore the behavior of Ca under pressure and find a number of new phases. Our structural sequence differs from the traditional picture for Ca, but is simila...

We investigated the stability of polymeric CO2 over a wide range of pressures, temperatures, and chemical environments. We find that the I-42d polymeric structure, consisting of a three-dimensional network of corner sharing CO4 tetrahedra, forms at 40-140 GPa and from a CO-N2 mixture at 39 GPa. An exceptional stability field of 0 to 286 GPa and 100 to 2500 K is documented for this structure, making it a viable candidate for planetary interiors. The stability of the tetrahedra...

Terrestrial exoplanets are of great interest for being simultaneously similar to and different from Earth. Their compositions are likely comparable to those of solar-terrestrial objects, but their internal pressures and temperatures can vary significantly with their masses/sizes. The most abundant non-volatile elements are O, Mg, Si, Fe, Al, and Ca, and there has been much recent progress in understanding the nature of magnesium silicates up to and beyond ~3 TPa. However, a c...

The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth's mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using ab initio evolutionary structure prediction, we find that only two m...

We investigate the effect of pressure, temperature and acidity on the composition of water-rich carbon-bearing fluids at thermodynamic conditions that correspond to the Earth's deep Crust and Upper Mantle. Our first-principles molecular dynamics simulations provide mechanistic insight into the hydration shell of carbon dioxide, bicarbonate and carbonate ions, and on the pathways of the acid/base reactions that convert these carbon species into one another in aqueous solutions...

Ternary C_{x}N_{y}O_{z} compounds are actively researched as novel high energy density and ultrahard materials. Although some synthesis work has been performed at ambient conditions, very little is known about the high pressure chemistry of of C_{x}N_{y}O_{z} compounds. In this work, first principles variable-composition evolutionary structure prediction calculations are performed with the goal of discovering novel mixed C_{x}N_{y}O_{z} materials at ambient and high pressure ...