We present the results of atomistic simulations using derived interatomic potentials for the pyrite-structured metal chalcogenides FeS(2), PtSb(2) and PtAs(2). Structural and elastic constants were calculated and compared with experimental measurements. Surface energies of low-index surfaces were calculated and closely reflected the measured stabilities of these compounds. Equivalent surfaces on the pyrite and marcasite structures of FeS(2) explained the experimentally observed intergrowths of the two phases.

We report first-principle electronic structure calculations of the three representative minerals of the platinum group: cooperite (PtS), braggite (PdPt3S4) and sperrylite (PtAs2) using the Tight-Binding Linear Muffin Tin Orbital (TB-LMTO) technique. We predict non-metallic behaviour for all three minerals with semiconductor band gaps of 1.31, 0.89 and 0.34 eV, respectively. In particular, our calculation is in excellent agreement with the experimental value of 1.4 eV deduced from diffuse-reflectance measurement for cooperite. We argue that the strong bonding between the Pt 5d and S(As) 3p(4p) states plays a crucial role in the formation of the semiconductor band gap.