Modelling of the thermal dependence of structural and elastic properties of calcite, CaCO3

A computational method, based on the quasiharmonic approximation, has been computer-coded to calculate the temperature dependence of elastic constants and structural features of crystals. The model is applied to calcite, CaCO3; an interatomic potential based on a C-O Morse function and Ca-O and O-O Born-type interactions, including a shell model for O, has been used. Equilibrations in the range 300-800 K reproduce the experimental unit-cell edges and bond lengths within 1%. The simulated thermal expansion coefficients are 22.3 (parallel to c) and 2.6 (perpendicular to c), against 25.5 and -3.7 x 10(-6) K-1 experimental values, respectively. The thermal coefficients of elastic constants tend to be underestimated; for the bulk modulus, -2.3 against -3.7 x 10(-4) K-1 is obtained.