First principles study of structural properties and electric field gradients in kaolinite

Abstract

This work reports a gauge-including projected augmented waves (GIPAW) method study of the structural and electronic properties of kaolinite (Al2Si2O5(OH)4). Different equilibrium structures were determined, and the corresponding electronic density of states and the electric field gradients (EFG) at each atomic site were calculated. The comparison of those predicted properties with measurements that come from neutron powder diffraction, single crystal synchrotron measurements, and nuclear magnetic resonance spectroscopies allowed a detailed study of the structure. In particular, the first principles calculations considered in this work cover different scales, going from the crystallographic structure to the atomic local environments, and serve as a tool to link both the structural and the hyperfine properties. This methodology predictions successfully solves a kaolinite structure in which the atomic local surroundings are consistent with the EFG measurements, thus providing answers to previous controversies between experimental studies about Al and Si local structures and the orientation of OH groups within the structure. In this sense, the GIPAW calculations support that kaolinite consists of asymmetrically distorted Si tetrahedra and Al octahedra sheets, and the interlayer OH groups are oriented nearly perpendicular to the layer.