Effects of intrinsic point defects on the structural, electronic, magnetic, and optical properties of marcasite FeS2

Systematic density functional theory calculations were carried out to study the structural, electronic, magnetic and optical properties of vacancy and antisite defects in marcasite FeS2 (m-FeS2). Five types of point defects were considered, that is S vacancy, Fe vacancy, FeS divacancy, Fe substitute S site and S substitute Fe site. The results show that Fe substitute S, S vacancy and Fe vacancy are the dominant defects in m-FeS2. The defects remarkably affect the electrical, optical performances of the m-FeS2, and even induce magnetism. All the considered point defects have defect states in the band gap of perfect m-FeS2. We estimated the stability of magnetic state and found that the m-FeS2 with point defects shows magnetic ground state except S vacancy case. Detailed analysis shows that m-FeS2 with S vacancy is a nonmagnetic semiconductor, with Fe vacancy, FeS divacancy and Fe substitute S site become magnetic metal while with S substitute Fe site is a magnetic semiconductor. In addition, compared with perfect m-FeS2, the static dielectric constants and static refractive indexes of m-FeS2 with defects are all increased significantly, the absorption coefficients show red shifts and enhancements in the infrared region due to the defect states.