A combined ab initio and photoelectron study of galena (PbS)

The results of a study of the physical, elastic and electronic properties of PbS using both first principles theoretical and experimental X-ray and ultraviolet photoelectron techniques are presented. We have investigated the influence of the computational approximations such as the basis set, pseudopotential and the treatment of exchange and correlation on the accuracy of the theoretical results. The current study work confirms that the binding energy of the S 3s state lies at 13 eV, in agreement with previous experimental work and contrary to earlier ab initio Hartree–Fock (HF) calculations. We establish that the reason for the discrepancy between previous experimental and theoretical determinations of the electronic structure of PbS is due to the treatment of the exchange interaction. We demonstrate that calculations using the HF approximation tend to overestimate the binding energies of the valence and core states yielding densities of states in poor agreement with experiment whereas calculations performed with density functional theory within either the local density or the generalised gradient approximation give a significantly better description of the electronic structure. Finally, we confirm that hybrid functional techniques such as B3LYP provide an excellent description of the physical and electronic structure of PbS.