Electronic structure of bulk and (0 0 1) surface layers of pyrite FeS2

The electronic structure of bulk and (0 0 1) surface layers of iron pyrite FeS2 have been calculated using a modern ab initio pseudo-potential method. For the bulk pyrite the calculated lattice constant, position parameter of sulfur, and band gap are in agreement with experimental values. For the (0 0 1) surface it is found that surface states form a conducting band. The conducting band and the conducting band tail of the bulk conduction manifold overlap and the width of the band gap is not influenced by the surface state. The surface states arise mainly from the iron 3d orbitals in the topmost layer with a smaller contribution from the sulfur 3p states. The relaxation of iron and sulfur atoms is found to be greatest in the top most layer. The surface energy is calculated to be equal to 1.063 J/m2.