Structural transition from marcasite to pyrite phase in FeSe2 under high pressure: a first-principles study

Abstract

Based on density functional theory, first-principles simulations and calculations are carried out to study the structural stability and electronic properties of FeSe2 under high pressure. Present theoretical calculations not only reproduce successfully the lattice constants, bulk modulus, and indirect band gap of both the marcasite and pyrite phases at ambient conditions, but also predict a first-order phase transition from the marcasite to pyrite structure at 9 GPa under compression. Based on elastic constants and phonon spectra calculations and detailed analysis of the geometry structures, a possible mechanism of the structural transformation from marcasite to pyrite structure is presented. Furthermore, pressure-induced band gap enlargement is observed in the marcasite phase, which is benefit for the optical applications. By contrast, the band gap of the pyrite phase gradually decreases along with the compression, and finally closes up due to the broadening of bandwidths.