Electronic and optical properties of the orthorhombic compounds FeX2 (X=P, As and Sb)

Abstract

• Electronic and optical properties calculations of FeX 2 (X = P, As and Sb) are carried out. • The mBJ gives a semiconducting state with an indirect energy gap of 0.248 eV for FeSb 2 . • The conduction band is due the d z 2 − r 2 states. • The imaginary part of the elements of the dielectric tensor has the same trend. • For FeAs 2 the LDA-calculated components of reflectivity reproduce the trend observed in the measured ones. First principles calculations, by means of the full-potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA), were carried out for the structural, electronic and optical properties of the orthorhombic compounds FeP 2 , FeAs 2 and FeSb 2 . The structural properties are determined through the total energy minimization and the relaxation of the internal parameters. The modified Becke–Johnson (mBJ) method is applied for the electronic structure of FeSb 2 . Our LDA-calculation shows that the first two compounds are indirect-gap semiconductors, while for the third one it predicts a small hole-pocket at the R point. The mBJ gives a semiconducting state with an indirect energy gap of 0.248 eV for FeSb 2 . The overall shape of the calculated imaginary parts of the dielectric tensor is similar for the three compounds. The assignment of the structures in the optical spectra and band structure transitions are investigated. The electronic dielectric constant along (0 1 0) direction is the largest for the three compounds. For FeAs 2 , the calculated components of reflectivity have the same trend of variation as the measured ones in the energy range 1.54–3.1 eV.