  Electronic and optical properties of semiconducting FeSe2 polymorphs
(marcasite and pyrite) were evaluated using density functional theory with
norm-conserving pseudopotential. Marcasite and pyrite of FeSe2 show indirect
band gaps of 0.86 eV and 0.67 eV respectively. Absorption coefficient is high
over a wide range of optical spectrum, indicating that these materials are
exploitable as solar cell absorber. Marcasite FeSe2 is found to be optically
anisotropic, whereas pyrite is isotropic. Mulliken Bond Population analysis
shows mixed ionic-covalent nature of bonding for both polymorphs. Effective
masses of electrons and holes were also calculated, which reinforce the
semiconducting nature of FeSe2
