Photoemission spectrum in paramagnetic FeO under pressure: Towards an ab initio description

Open Access

Photoemission spectrum in paramagnetic FeO under pressure: Towards an ab initio description

S. Di Sabatino, J. Koskelo, J. A. Berger, and P. Romaniello

Phys. Rev. Research 3, 013172 – Published 22 February 2021

Abstract

In this paper we provide an exhaustive study of the photoemission spectrum of paramagnetic FeO under pressure using a refined version of our recently derived many-body effective energy theory (MEET). We show that, within a nonmagnetic description of the paramagnetic phase, the MEET gives an overall good description of the photoemission spectrum at ambient pressure as well as the changes it undergoes by increasing pressure. In particular at ambient pressure the band gap opens between the mixed Fe $t_{2 g}$ and O $2 p$ states and the Fe $4 s$ states and, moreover, a $d − d$ gap opens, which is compatible with a high-spin configuration (hence nonzero local magnetic moments as observed in experiment), whereas with decreasing pressure the band gap tends to close, $t_{2 g}$ states tend to become fully occupied, and $e_{g}$ states tend to become fully unoccupied, which is compatible with a low-spin configuration (hence a collapse of the magnetic moments as observed in experiment). This is a remarkable result, since, within a nonmagnetic description of the paramagnetic phase, the MEET is capable to correctly describe the photoemission spectrum and the spin configuration at ambient as well as high pressure. For comparison we report the band-gap values obtained using density-functional theory with a hybrid functional containing screened exchange (HSE06) and a variant of the $G W$ method (self-consistent COHSEX), which are reliable for the description of the antiferromagnetic phase. Both methods open a gap at ambient pressure, although, by construction, they give a low-spin configuration; increasing pressure they correctly describe the band-gap closing. We also report the photoemission spectrum of the metallic phase obtained with one-shot fully dynamical $G W$ on top of the local-density approximation, which gives a spectrum very similar to dynamical mean-field theory results from literature.

Received 25 February 2020
Revised 22 December 2020
Accepted 26 January 2021

DOI:https://doi.org/10.1103/PhysRevResearch.3.013172

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Density of states Electronic structure

Band structure methods Density functional theory First-principles calculations GW method Green's function methods

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Di Sabatino ^1,2, J. Koskelo ¹, J. A. Berger ², and P. Romaniello ^1,*

¹Laboratoire de Physique Théorique, Université de Toulouse, CNRS, UPS and ETSF, France
²Laboratoire de Chimie et Physique Quantiques, Université de Toulouse, CNRS, UPS and ETSF, France

^*pina.romaniello@irsamc.ups-tlse.fr

Article Text

Click to Expand

References

Click to Expand

Issue

Vol. 3, Iss. 1 — February - April 2021

Subject Areas

Condensed Matter Physics

Reuse & Permissions

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
$MEET + LDA$ $k$ -resolved and total spectral functions. Removal (circles) and addition energies (triangles) are reported along high-symmetry directions for relative volumes $V / V_{0} = 1$ (a) and $V / V_{0} = 0.6$ (b), where $V_{0}$ is the equilibrium volume at ambient pressure. We also report the LDA band structure (black dotted line). The contributions of the Fe $t_{2 g}$ and $e_{g}$ states and of the O $2 p$ states to the total spectral function are also reported. The experimental photoemission spectrum (small circles) is taken from Ref. [25].
Reuse & Permissions
Figure 2
Left panel: Occupancies of $t_{2 g}$ (blue) and $e_{g}$ (cyan) orbitals at relative volume $V / V_{0} = 1$ (solid line and filled circles) and $V / V_{0} = 0.6$ (dashed line and open squares) as a function of the power functional parameter $α$ . We report also the average $d$ occupancy (black). In the right panel the ratio between $e_{g}$ and $t_{2 g}$ occupancies is plotted. Values of the ratio $n_{e_{g}} / n_{t_{2 g}}$ are extracted from Ref. [13] and reported as horizontal lines.
Reuse & Permissions
Figure 3
$k$ -resolved spectral function of FeO: $MEET + LDA$ energies are reported along high-symmetry directions and compared with DMFT results from Ref. [13] for ambient (a) and high pressure (b). We also report LDA band structures (white solid line) which are used to align the MEET energies. Note that for a meaningful comparison we have used for MEET and LDA calculations the same lattice constant used in Ref. [13].
Reuse & Permissions
Figure 4
Photoemission spectrum calculated using MEET (i.e., without the alignment with LDA) for various values of $α$ for $V / V_{0} = 1$ (a) and $V / V_{0} = 0.6$ (b). The contributions of the Fe $t_{2 g}$ and $e_{g}$ states and of the O $2 p$ states to the total DOS are also reported.
Reuse & Permissions
Figure 5
Quasiparticle band structure (red dots) and spectral function (red solid line) within $G_{0} W_{0}$ at $V / V_{0} = 0.6$ . For comparison we report also the LDA band structure and DOS (dotted black line).
Reuse & Permissions
Figure 6
Upper panel: Spectral function calculated with the full dynamical $G_{0} W_{0}$ (black solid line). For Fe $3 d$ states we report also the partial spectral function (blue dot-dashed line) and the QP spectral function (red dashed line). We notice that, for comparison, the QP spectrum has been corrected introducing the corresponding renormalization factor $Z_{i}$ which on average is 0.64 for the Fe $3 d$ bands. Middle and bottom panels: Spectral function $A_{i} (ω)$ (solid black line), $ω - ε_{i}^{0} - Re Σ_{i} (ω)$ (red dashed line), and $Im Σ_{i} (ω)$ (blue dotted line) for the Fe $e_{g}$ states at the $Γ$ and $L$ points. The quasiparticle energy $ε_{i}^{QP}$ is given by the solution of the equation $ω - ε_{i}^{0} - Re Σ_{i} (ω) = 0$ .
Reuse & Permissions

Physical Review Research