# Structures and stability of calcium and magnesium carbonates at mantle pressures

C. Pickard, R. Needs

*Physical Review B* 91, 104101 (2015)

#highpressure#condensedmatter#molecularstructure

Predicting stable structures of calcium and magnesium carbonate is crucial for understanding the Earth's deep carbon cycle.

Ab initio random structure searching (AIRSS) and density functional theory methods are used to predict structures of calcium and magnesium carbonate (CaCO3 and MgCO3) at high pressures. We find a previously unknown CaCO3 structure which is more stable than the aragonite and "post aragonite" phases in the range 32--48 GPa. At pressures from 67 GPa to well over 100 GPa the most stable phase is a previously unknown CaCO3 structure of the pyroxene type with fourfold coordinated carbon atoms. We also predict a stable structure of MgCO3 in the range 85--101 GPa. Our results lead to a revision of the phase diagram of CaCO3 over more than half the pressure range encountered within the Earth's mantle, and smaller changes to the phase diagram of MgCO3. We predict CaCO3 to be more stable than MgCO3 in the Earth's mantle above 100 GPa, and that CO2 is not a thermodynamically stable compound under deep mantle conditions. Our results have significant implications for understanding the Earth's deep carbon cycle.

#### Phase transition creates the geometry of the continuum from discrete space

R. Farr, T. Fink

*Physical Review E*

#### The statistical physics of real-world networks

G. Cimini, T. Squartini, F. Saracco, D. Garlaschelli, A. Gabrielli, G. Caldarelli

*Nature Reviews Physics*

#### On defining the Hamiltonian beyond quantum theory

D. Branford, O. Dahlsten, A. Garner

*Foundations of Physics*

#### Reconstructing grain-shape statistics from electron back-scatter diffraction microscopy

R. Farr, Z. Vukmanovic, M. Holness, E. Griffiths

*Physical Review Materials*

#### Tackling information asymmetry in networks: a new entropy-based ranking index

P. Barucca, G. Caldarelli, T. Squartini

*Journal of Statistical Physics*

#### Eigenvalues of subgraphs of the cube

B. Bollobás, J. Lee, S. Letzter

*European Journal of Combinatorics*

#### Maximum one-shot dissipated work from Rényi divergences

N. Halpern, A. Garner, O. Dahlsten, V. Vedral

*Physical Review E *

123 / 123 papers