Elastic properties of heterodesmic composite structures: The case of calcite CaCO3 (space group R3¯c)

Composite-like structures are commonly found in nature and, among them, calcite (CaCO3, space group R-3c) is made of alternately stacked layers of Ca2+ and triangular CO32- ions. The bonding scheme of this mineral results in an heterodesmic structure because the carbonate ions are made up of covalent bonds (acting along the crystallographic a- and b-axes) and the positive Ca2+ and negative CO32- layers are held together by electrostatic interactions (along the c-axis). Because of its structure and heterodesmic nature, calcite is a highly anisotropic material suitable as a test case to design, develop and assess the quality of theoretical approaches to model composite-like structures. In the present work, the structural and elastic properties (second-order elastic constants and equation of state) of calcite have been investigated by means of the Density Functional Theory, comparing several Hamiltonians and specific a posteriori corrections to treat the weak long-range interactions. Both second-order elastic moduli and the equation of state of calcite were obtained and discussed in comparison to well-established experimental data. The results and the approach presented in this in silico work could be of use for the characterization of elastic properties of other similar minerals/crystal structures used in composites for structural applications.