X-ray diffractometer, FTIR and theoretical approach of topological analysis of covellite single crystal

Abstract

Covellite (CuS) is a mineral sulfide with a multitude of potential applications in various technical fields. While it possesses a basic formula, its structure is complex, featuring alternating layers of planar CuS3 triangles and CuS4 tetrahedrons interconnected by S–S bonds. To gain a deeper understanding of Covellite's structural, mechanical and electrical properties, as well as its chemical bonding, extensive research utilizing X-ray diffractometer, FTIR and first-principles calculations have been conducted on its covalent Structure (CuS). The DFT and DFT + U methods were employed, revealing their sensitivity to the correlation treatment (U value). Although a universal U value cannot be determined, this investigation identifies U = 5.5 eV as an appropriate quantity. The examination of the electronic structure uncovers a significant metallic character attributable to the p(S)-d(Cu) orbital interactions up to the Fermi level. Moreover, the estimated density of states illustrates that the atomic contribution primarily arises from the 3d1 orbitals, which ultimately induce the [2D] plane conductivity anisotropy of Covellite. Additionally, the electron density underwent a topological analysis using the Quantum ESPRESSO PW software, leading to the computation of two distinct topological charges associated with Cu. This finding substantiates the presence of an iconic model featuring mixed charges. The covalent nature of the S–S bond receives support from the DFT analysis, and it is plausible that the preferential cleavage of CuS occurs at the [2D] surface, specifically at the CuS bond. It is worth noting that the S atoms constitute the majority of the cell volume and possess a dominant influence on the crystal's compressibility.