PHYSICAL REVIEW B 86, 235202 (2012) Pressure-induced metal-insulator transition and absence of magnetic order in FeGa 3 from a first-principles study J. M. Osorio-Guill´ en * Instituto de F´ ısica, Universidad de Antioquia, Medell´ ın, Colombia and Centro de Ciˆ encias Naturais e Humanas, Universidade Federal do ABC, Santo Andr´ e, SP, Brazil Y. D. Larrauri-Pizarro and G. M. Dalpian Centro de Ciˆ encias Naturais e Humanas, Universidade Federal do ABC, Santo Andr´ e, SP, Brazil (Received 13 September 2012; published 3 December 2012) The intermetallic compound FeGa 3 is a narrow-gap semiconductor with a measured gap between 0.2 and 0.6 eV. The presence of iron d states on the top of the valence band and on the bottom of the conduction band, together with its moderate electronic correlation (U/W ∼ 0.6), have led to the question of whether there is magnetic order in this compound. We have examined the possible presence of magnetism in FeGa 3 as well as its electronic structure at high pressures, using the density functional theory (DFT) + U method with the intermediated double-counting scheme. We have found that for an optimized value of the Yukawa screening length λ, there is no magnetic moment on the iron ions (μ = 0), implying that FeGa 3 is nonmagnetic. We have also found that around a pressure of 25 GPa a metal-insulator transition takes place. DOI: 10.1103/PhysRevB.86.235202 PACS number(s): 71.20.Nr, 71.30.+h, 31.15.V− I. INTRODUCTION Intermetallic narrow-gap semiconductors have very in- teresting electronic, magnetic, thermoelectric, and transport properties. 1–15 Among these compounds, FeGa 3 (which has the Fe d states on the top and the bottom of the valence and conduction bands, respectively) has emerged as an attractive compound to study the regime between weakly and strongly correlated materials. 5–8,11–15 On one hand, some experimental measurements of the conductivity, magnetic susceptibility, M¨ ossbauer spectra, specific heat, etc., have not shown distinctive features of a very strong electronic correlation, and these results also indicate the absence of magnetism in this compound. 10,11 Nevertheless, the size of the ratio between the on-site Coulomb interaction (characterized by the Hubbard U parameter) and the bandwidth of the Fe d electrons (U/W ∼ 0.6) is comparable to other correlated materials. 5,8,14,16,17 These clues have led to a first-principles density functional theory (DFT) + U study of the magnetic order in this compound, showing evidence of a “spin-singlet” coupled Fe dimer with antiferromagnetic (SS-AF) order (with a magnetic moment of 0.63μ B /Fe ion for Hubbard U = 2 eV). These results were obtained using the fully localized atomic limit (FLL) for the double-counting (DC) term for DFT + U . 8 A recent muon spin rotation measurement suggests that the existence of a spin polaron band is consistent with the SS-AF scenario, in which Fe moments exist at all temperatures. 3 How- ever, due to the moderate electronic correlation in this material, the FLL is not appropriate to study this compound, and it could lead to an erroneous magnetic ordered solution. 16,18 It is pertinent to reexamine the possible presence of magnetic order in this compound using DFT + U with a suitable DC scheme for systems presenting weak to moderate elec- tronic correlation, such as the intermediate double counting (INT DC). 17,18 On the other hand, it is known that low-electron doping tremendously modifies the electronic and magnetic properties of FeGa 3 . 6,7 Remarkably, electron doping of this compound induces a crossover to metallic behavior and shows some physical properties that resemble strongly correlated metals. Also, Co doping creates local magnetic moments, presumably on Co ions, but there is not a conclusive explanation of the mechanism that triggers the occurrence of magnetic order in this compound. 7 The effect of external pressure provides a very useful means to modify the strength of the hybridization between the Fe d and Ga s and p states, making it possible to study systematically the electronic and magnetic structure without introducing any chemical perturbation, charge carri- ers, or defects. While some chemical substitution studies of FeGa 3 have revealed a metal-insulator transition (MIT) due to electron doping, 6,7 the effect of volume compression has not been employed yet. In this work we show that in FeGa 3 there is no presence of SS-AF and propose that the application of an external pressure on this compound changes its electronic structure profoundly, causing a MIT around 25 GPa. II. METHOD OF CALCULATION Spin-polarized first-principles DFT and DFT + U calcula- tions have been carried out using the full-potential augmented- plane-wave method with local orbitals (FP-APW + lo) as implemented in the ELK code. 19 For the exchange-correlation energy functional we have employed the generalized gradient approximation (GGA). 20 The DFT + U approach is applied following the methodology described in Ref. 18 with Yukawa screening 16,18,21 and the INT-DC scheme. 17,18 In this DFT + U implementation one adds a Hartree-Fock correction to the DFT-GGA Hamiltonian, where the kernel of the interaction term is the bare Coulomb interaction (1/r 12 ). One can choose an atomic basis function to evaluate the interaction term, allowing us to write down the radial part of the Coulomb interaction by the bare Slater integrals F (k) . These F (k) are mostly affected by screening effects, and one should replace them by the screened Slater integrals F (k) I , which are the pa- rameters of the DFT + U scheme. These F (k) I can be obtained 235202-1 1098-0121/2012/86(23)/235202(6) ©2012 American Physical Society