First-principles investigation of the optical properties of layered phyllosilicates

Naturally occurring phyllosilicates such as talc and kaolinite-type minerals represent intrinsic layered two-dimensional insulators with highly anisotropic electronic and optical properties. In this work, we perform a comparative first-principles study of talc and kaolinite, along with its structural polymorphs dickite and nacrite, using density functional theory within the PBE-GGA framework. Structural relaxations, electronic band structures, and frequency-dependent dielectric functions were calculated to further analyze the effect of interlayer bonding on optical response. Talc, stabilized by van der Waals interlayer interactions, exhibits pronounced optical anisotropy with sharper ultraviolet absorption features, whereas kaolinite-type minerals, characterized by interlayer hydrogen bonding, display enhanced dielectric polarization along the direction normal to the layered planes and broader absorption spectra. The results demonstrate a direct link between interlayer coupling and optical anisotropy in layered phyllosilicates, highlighting their potential as natural wide-gap dielectric materials for photonic and optoelectronic applications.