Spectrum for Nonmagnetic Mott Insulators from Power Functional within Reduced Density Matrix Functional Theory

Abstract

A fully first principles theory capable of treating strongly correlated solids remains the outstanding challenge of modern day materials science. This is exemplified by the transition metal oxides, prototypical Mott insulators, that remain insulating even in the absence of long range magnetic order. Capturing the non-magnetic insulating state of these materials presents a difficult challenge for any modern electronic structure theory. In this paper we demonstrate that reduced density matrix functional theory, in conjunction with the power functional, can successfully treat the nonmagnetic insulating state of the transition metal oxides NiO and MnO. We show that the electronic spectrum retains a gap even in the absence of spin order. We further discuss the detailed way in which RDMFT performs for Mott insulators and band insulators, finding that for the latter occupation number minimization alone is required, but for the former full minimization over both occupation numbers and natural orbitals is essential.

Reduced density-matrix functionals applied to the Hubbard dimer

“…Approximations for ionization potentials 56 and spectral functions 31 have been introduced on top of rDMFT. The latter method on the one hand yields spectra that agree well with experimental results for transition metal oxides 31,49,50 for particular choices of the power functional parameter. On the other hand investigations on the Hubbard dimer 30 suggest caution and claim that the underlying physics is not correctly treated.…”

Photoemission spectra from reduced density matrices: The band gap in strongly correlated systems

“…However, contrary to us, the authors of Ref. 44 use a shift of the k-point grid. With the shift of the k-point grid the number of inequivalent k points in the irreducible Brillouin zone is higher than in the case without shift and the calculations should converge faster.…”

Reduced density-matrix functionals from many-particle theory

“…It should be noted here, that the band gap was estimated by an extrapolation technique [67] due to the missing derivative discontinuity. Applications to transition metal oxides investigated the parameter dependence [68,69] as well as metal-insulator transitions [70,71] and showed good agreement with other methods. However due to the antiferromagnetic ground state of the transition metal oxides under investigation, the pathologies of the power functional for the prediction of magnetic structures did not become apparent.…”