Internal Relaxation, Band Gaps and Elastic Constant Calculations of FeS2

Abstract

Full relaxation of volume and internal parameters of iron pyrite and marcasite FeS2, has been studied using a plane-wave pseudopotential method within the Local Density Approximation to Density Functional Theory (LDA-DFT). We find that the internal parameter u of pyrite decreases with hydrostatic compression. The P-V equation of state falls slightly closer to the experimental curve than a previous unrelaxed Tight-Binding Linear Muffin-Tin Orbital (TB-LMTO) calculation. The optimized parameters are used in a TB-LMTO calculation to predict the electronic structure from which we find a larger band gap on marcasite compared to pyrite. Ab initio calculations of elastic constants for pyrite were performed using the Full Potential (FP) LMTO method and agree to within 7% with experiment.