Self-energies in itinerant magnets: A focus on Fe and Ni

Abstract

We present a detailed study of local and nonlocal correlations in the electronic structure of elemental transition metals carried out by means of the quasiparticle self-consistent GW (QSGW) and dynamical mean field theory (DMFT). Recent high resolution ARPES and Haas-van Alphen data of two typical transition metal systems (Fe and Ni) are used as a case study. (i) We find that the properties of Fe are very well described by QSGW. Agreement with cyclotron and very clean ARPES measurements is excellent, provided that final-state scattering is taken into account. This establishes the exceptional reliability of QSGW also in metallic systems. (ii) Nonetheless QSGW alone is not able to provide an adequate description of the Ni ARPES data due to strong local spin fluctuations. We surmount this deficiency by combining nonlocal charge fluctuations in QSGW with local spin fluctuations in DMFT. (iii) Finally we show that the dynamics of the local fluctuations are actually not crucial. The addition of an external static field can lead to similarly good results if nonlocal correlations are included through QSGW.

Questaal: A package of electronic structure methods based on the linear muffin-tin orbital technique

“…30). Our QSGW +DMFT implementation can be successfully applied to a wide range of systems; weakly correlated metals [112], strongly correlated metals [179] and correlated Mott insulators [83].…”

“…• The original formulation of Quasiparticle Self-Consistent GW [16], demonstration of its wide applicability [80], and a detailed description [81] • Questaal's implementation of nonequilibrium electron transport in nanosystems [14], and significant applications to magnetic transport [191,21,192,23,24] • A fusion of genetic algorithms and exchange interactions to predict and optimise critical temperatures in multi-component systems [176] • Dressselhaus terms calculated ab initio with high fidelity in zincblende semiconductors [104,193,106] • First GW description of 4f systems, showing the tendency to overestimate splitting between occupied and unoccupied f states [131] • Spin wave theory within QSGW [107] • Prediction of Impact Ionisation rates with QSGW [110] • The PMT method of Sec. 3.10 [53] • A formulation of tunnelling transport within QSGW [109] • Effect of spin-orbit coupling on the QSGW selfenergy [74] • Approximate description of transient absorption spectroscopy within QSGW [194] • Questaal's first application of QSGW +DMFT, showing the need to go beyond GW when spin fluctuations are important [112].…”

Consistent partial bosonization of the extended Hubbard model

“…However, an account for vertex corrections beyond the dynamical mean-field solution is desirable [66][67][68]. Especially, it is an important problem for description of spin fluctuations and magnetic polarization in realistic systems [69,70] as they are not captured by a standard GW+DMFT scheme [35][36][37][38][39][40][41]. While the use of the fermion-boson vertex in a diagrammatic solution of multiband problems is possible [44], an inclusion of the fermion-fermion vertex in realistic calculations is extremely challenging and time consuming numerically [29][30][31][32][33][34].…”

ComDMFT: A massively parallel computer package for the electronic structure of correlated-electron systems

“…For the construction of H MF , various static mean-field approaches have been suggested and tested, ranging from one-shot GW [64,65], screened exchange [68], LQSGW [70] and QSGW [89]. In addition, the idea of the non-local version of QSGW and LQSGW was proposed [67].…”