Compressional behavior of the aragonite-structure carbonates to 6 GPa

Abstract

AbstractThe behaviors of aragonite (CaCO$$_3$$3), strontianite (SrCO$$_3$$3), cerussite (PbCO$$_3$$3), and witherite (BaCO$$_3$$3) at increasing pressure have been studied up to 6 GPa using density functional theory with plane waves. A parallelism of the orthorhombic carbonates with the closed-packed AsNi structure is considered in our analysis, being the CO$$_3^{2-}$$32-groups not centered in the interstice of the octahedron. The decomposition of the unit-cell volume into atomic contributions using the Quantum Theory of Atoms in Molecules has allowed the analysis of the bulk modulus in atomic contributions. The bulk, axes, interatomic distances, and atomic compressibilities are calculated. The largest compression is on theccrystallographic axis, and theclinear modulus has a linear function with the mineral bulk modulus ($$K_0$$K0). Many of the interatomic distances moduli of the alkaline earth (AE) carbonates show linear functions with the bulk modulus; however, the whole series (including cerussite) only gives linear functions when$$K_0$$K0is related either with theCCdistances modulus or the modulus of the distances of theCto the faces of the octahedron perpendicular toc. These last distances are the projections of the Metal–Oxygen (MO) distances to the center of the octahedron.$$K_{0AE}$$K0AEcarbonates also show linear functions with the atomic moduli of their cations. However, the whole series show a linear relation with the atomic modulus ofCatoms. Therefore, the whole series highlight the importance of theCatoms and their interactions in the mechanism of compression of the orthorhombic carbonate series.