Ab initiostudy on the rare-earth iron-pnictides RFeAsO (R = Pr, Nd, Sm, Gd) in the low-temperatureCmmaphase

Abstract

We present density functional theory calculations on the iron-based pnictides RFeAsO (R = Pr, Nd, Sm, Gd). The calculations have been carried out using plane waves and the projector augmented wave (PAW) pseudopotential approach. Structural, magnetic and electronic properties are studied within the generalized gradient approximation (GGA) and also within GGA + U in order to investigate the influence of electron correlation effects. The low-temperature Cmma structure is fully optimized by the GGA considering both non-magnetic and magnetic cells. We have found that the spin-polarized structure improves the agreement with experiments on equilibrium lattice parameters, particularly the c lattice parameter and the Fe-As bond-lengths. The electronic band structure, total density of states, and spin-dependent orbital-resolved density of states are also analyzed and discussed in the frameworks of GGA and GGA + U. For all materials, by including an on-site Coulomb correction, the rare-earth 4f states move away from the Fermi level and the Fermi level features of the systems are found to be mostly defined by the 3d electron-electron correlations in Fe.

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“…Among them, Sr 0.5 Sm 0.5 FFeAs has the highest [48]. (d) GGA+U electronic band structure of PrFeAsO [49]. The Fermi level is set to zero.…”

“…Reprinted (figure) with permission from [48], Copyright (2008) by the American Physical Society. Reproduced from [49]. © IOP Publishing Ltd. All rights reserved.…”

“…Among the 122 phase compounds of FeAs, Pr-doped CaFe 2 As 2 has the highest superconducting critical temperature of 49 K [62]. Figure 5(d) indicates that iron-based superconductor PrFeAsO is a pseudo-metal superconductor due to its semiconductor band [49]. In recent years, other complex iron-based superconducting materials listed in figure 5 have also been successfully synthesized experimentally, but no new iron-based superconductors with higher T c have been discovered [20].…”

“…(c) Electrical resistance of BaFe 2 As 2 , KFe 2 As 2 and (Ba 0.6 K 0.4 )Fe 2 As 2[48]. (d) GGA+U electronic band structure of PrFeAsO[49]. The Fermi level is set to zero.…”