Investigation on Atomic Structure and Mechanical Property of Na- and Mg-Montmorillonite under High Pressure by First-Principles Calculations

Montmorillonite is an important layered phyllosilicate material with many useful physicochemical and mechanical properties, which is widely used in medicine, environmental protection, construction industry, and other fields. In order to a get better understanding of the behavior of montmorillonite under high pressure, we studied its atomic structure, electronic and mechanical properties using density functional theory (DFT), including dispersion corrections, as function of the interlayer Na and Mg cations. At ideal condition, the calculations of lattice constants, bond length, band structure, and elastic modulus of Na- and Mg-montmorillonite are in good agreement with the experimental values. Under high pressure, the lattice constants and major bond lengths decreased with increasing pressure. The calculated electronic properties and band structure show only a slight change under 20 GPa, indicating that the effect of pressure on the electronic properties of Na- and Mg-montmorillonite is weak. The bulk modulus, shear modulus, Young's modulus, shear wave velocity and compression wave velocity of Na- and Mg-montmorillonite are positively correlated with the external pressure, and the other mechanical parameters have a little change. The calculated studies will be useful to explore experiments in the future from a purely scientific point of view.