Structural and Elastic Behaviour of Sodalite Na₈(Al₆Si₆O₂₄)Cl₂ at High-Pressure by First-Principle Simulations

Abstract

Sodalite Na8(Al6Si6O24)Cl2 (space group P4¯3n) is an important mineral belonging to the zeolite group, with several and manyfold fundamental and technological applications. Despite the interest in this mineral from different disciplines, very little is known regarding its high-pressure elastic properties. The present study aims at filling this knowledge gap, reporting the equation of state and the elastic moduli of sodalite calculated in a wide pressure range, from −6 GPa to 22 GPa. The results were obtained from Density Functional Theory simulations carried out with Gaussian-type basis sets and the well-known hybrid functional B3LYP. The DFT-D3 a posteriori correction to include the van der Waals interactions in the physical treatment of the mineral was also applied. The calculated equation of state parameters at 0 GPa and absolute zero (0 K), i.e., K0 = 70.15(7) GPa, K’ = 4.46(2) and V0 = 676.85(3) Å3 are in line with the properties derived from the stiffness tensor, and in agreement with the few experimental data reported in the literature. Sodalite was found mechanically unstable when compressed above 15.6 GPa.

Keywords

• sodalite
• zeolite group
• equation of state
• stiffness tensor
• seismic wave velocities
• DFT