Molecular Dynamics Simulations of Structural and Mechanical Properties of Muscovite: Pressure and Temperature Effects

Layered minerals comprise a large fraction of the soils and crustal rocks on Earth, and knowledge of their anisotropic mechanical properties is essential for many varied applications including underground storage of waste materials, monitoring seismic response, drilling activities, and development of novel nanocomposite materials. Results of molecular dynamics simulations for the elastic and structural properties of muscovite are obtained as a function of temperature, pressure, and strain. Three different temperatures (T = 298, 500, and 800 K), pressures ranging from atmospheric pressure to 15 GPa, and strains up to 10% are used to derive mechanical properties of muscovite. Bulk moduli are calculated from NPT simulations with hydrostatic pressure, whereas the Young's moduli, shear moduli, and Poisson's ratios are calculated from stress strain curves generated at relatively slow rates of deformation. Simulation results obtained for room-temperature mechanical properties are in good agreement with reported experimental values, although the model consistently overestimates the in-plane elastic response. In general, the results demonstrate that elastic properties of muscovite depend on both temperature and pressure, with elastic constants exhibiting a small, statistically significant decrease as temperature is increased. Bulk moduli exhibit a decrease with increasing temperature and an increase with increasing pressure, whereas temperature has no statistically significant impact on the Poisson's coefficients. Finally, structural data obtained from radial distribution functions and power spectra indicate a slight shift of the interlayer potassium ions into the siloxane cavities with increasing pressure.