First-principles study of electronic structure and fermiology of covellite mineral and its B1, B3 phases

We present the first-principles calculations under the framework of density functional theory to explore the Fermi surface and electronic properties of covellite mineral. The correlation effects are considered applying the +U correction in the density functional theory. Lattice parameters are determined and the possibility of pressure induced phase transitions to the hypothetical B1 and B3 crystals is examined. All calculations show impending B18 → B1 and B3 → B1 phase transitions. Using generalized gradient approximation these are found to occur at 7.4 and 6.48 GPa, respectively. Electronic bands structures of the three crystals highlight metallic properties. Two copper atoms situated at distinct locations in covellite exhibit a distinct role. The Fermi surfaces of all phases are presented. The calculations of B18 map out corrugated cylindrical Fermi surface signifying inter-layer interaction mediated by the S(II)-S(II) bond. The +U correction shows anisotropy in the Fermi surface noted in experiment. It also indicates stronger inter-layer interaction. Applying Debye-Slater and the Debye-Grüneisen models the thermal expansion coefficient, heat capacity and entropy are found and their temperature dependence is discussed.