A New Transferable Forcefield for Simulating the Mechanics of CaCO3 Crystals

Many sets of forcefield parameters for calcium carbonate (CaCO3) and CaCO3–water interactions have been developed for thermodynamic calculations, but growing interest in modeling the molecular-scale mechanics of biomineral nanocomposite materials such as nacre has led to a need for interaction parameters that accurately model the anisotropic mechanical properties of CaCO3. A novel forcefield for aragonite, one polymorph of CaCO3, has been fitted to the structure and elastic constants of the mineral, and the validation of these interaction parameters demonstrates that the forcefield can well capture the shear and elastic moduli of aragonite and also performs well when transferred to other CaCO3 polymorphs. The corresponding aragonite–water and aragonite–protein parameters are also obtained and utilized in force probe molecular dynamics (FPMD) simulations of the forced desorption of an acidic polypeptide from an aragonite crystal surface, resulting in a rupture force of roughly 60 pN per amino acid residue at pulling speeds characteristic of Atomic Force Microscope experiments. Our forcefield for CaCO3 and CaCO3–protein interactions can be applied to study the physical and mechanical properties of organic–inorganic composite systems, especially for the next generation of bionanocomposite materials.