Electronic structure, chemical bonding, and hyperfine parameters in layered silicates

The electronic structure of metal sites in 2:1 layer silicates was calculated employing the first-principles self-consistent discrete variational embedded cluster method, in the framework of density-functional theory. Densities of states, charge and spin densities, electric-field gradients, and magnetic fields were obtained for octahedral Fe²⁺ sites in annite and compared with experimental measurements. The chemical environment for tetrahedral M sites (M=Al³⁺ and Si⁴⁺) was also studied to determine atomic configurations and bonding structures. Cluster-size effects were investigated by systematically expanding the number of coordination shells included in the variational region.