Elasticity constants of clay minerals using molecular mechanics simulations

Abstract

The purpose of this paper is to obtain the elasticity constants (including the volume and shear modulus, Young modulus, and Poisson’s ratio) of clay minerals, or montmorillonite, kaolinite and illite, using the molecular mechanics simulations. The Lennard-Jones potential function and Ewald summation method were respectively used to compute the Van der Waals’ and Coulomb forces. The integrated approach was made to perform the energy optimization of the mineral crystals. The unit and super cells of each mineral were then established to compute the elasticity constants of clay minerals. The substitutions, structural waters and anisotropy were also considered during the simulations. It shows that the montmorillonite easily move laterally while kaolinite is reasonably stable under vertical load; the substitution plays an important role for the elasticity constants of illite; the bulk modulus, shear modulus, Young’s modulus decrease if the number of waters increases; the intrinsical anisotropy occurred in the clay minerals; montmorillonite and illite may expand under external load.