Quasiparticle Band Structure of Iron Pyrite*

Being a non-toxic and abundant material, iron pyrite (FeS₂) is an attractive material for photovoltaic applications with a very high quantum efficiency and absorption coefficient. Despite much research effort, the fundamental band gap of FeS₂ is still not accurately determined. The measured fundamental band gap of FeS₂ ranges from 0.84 to 1.2 eV. Surprisingly, straightforward density functional theory calculations within the generalized gradient approximation (GGA) predict a band gap of 0.46 eV, whereas the supposedly more accurate Heyd-Scuseria-Ernzerhof (HSE) hybrid functional predicts a band gap of 2.6 eV. Perhaps more intriguing is that it was reported [1] that quasiparticle calculations within the GW approximation predicts a band gap of 0.3 eV for FeS₂. In this work, we report fully converged G₀W₀ quasiparticle band structure of FeS₂ using a recently developed accelerated method [2]. Contrary to the previous claim, our results predict a 0.81 eV (dipole forbidden) band gap at the Gamma point and a dipole allowed transition energy of about 1.07 eV. Our work illustrates the importance of the convergence issue in GW calculations .