Diffusion Monte Carlo: A pathway towards an accurate theoretical description of manganese oxides

Saritas, Kayahan; Krogel, Jaron T.; Kent, Paul; Reboredo, Fernando A.

doi:10.1103/physrevmaterials.2.085801

Cited by 18 publications

(26 citation statements)

References 119 publications

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“…This agrees very well with the photoluminescence and UV/Vis [125,126] experiments and also with PBE0, where a band gap of 3.2-3.3 eV is obtained using QE-RRKJ and CRYSTAL-LCAO. DMC band gaps are larger than the hybrid-DFT band gaps as observed previously [32,46,87]. We used a simple single-determinant scheme to obtain the band gaps from DMC; therefore, our results should be treated as an upper bound due to the fixed node bias, which may not fully cancel between the ground and excited states.…”

Section: Electronic Structure Quasiparticle and Optical Gapsmentioning

confidence: 78%

“…However, the accuracy of DFT has not yet been sufficient to differentiate between the two mechanisms [4,7]. Projector methods [24], such as Diffusion Monte Carlo (DMC) [25,26], are shown to be the most accurate and practical methods to tackle the ground states of complex, highly correlated materials with a similar success in the excited states [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Although it is computationally more expensive, DMC explicitly accounts for the antisymmetry of the many-body wave function and electron correlation, without using any empirical parameters [25,26,44,45].…”

Section: Introductionmentioning

confidence: 99%

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Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Saritas

Krogel

Okamoto

et al. 2019

Phys. Rev. Materials

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Magnetism in lanthanum cobaltite (LCO, LaCoO3) appears to be strongly dependent on strain, defects, and nanostructuring. LCO on strontium titanate (STO, SrTiO3) is a ferromagnet with an interesting strain relaxation mechanism that yields a lattice modulation. However, the driving force of the ferromagnetism is still controversial. Experiments debate between a vacancy-driven or straindriven mechanism for epitaxial LCO's ferromagnetism. We found that a weak lateral modulation of the superstructure is sufficient to promote ferromagnetism. Our research also showed that ferromagnetism appears under uniaxial compression and expansion. Although earlier experiments suggest that bulk LCO is nonmagnetic, our Diffusion Monte Carlo calculations found that magnetic phases have a lower energy ground state for bulk LCO. This article discusses recent experiments indicating a more complicated picture for the bulk magnetism and closer agreement with our calculations. The role of defects are also discussed through excited-state calculations. arXiv:1908.02811v3 [cond-mat.mtrl-sci]

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Section: Electronic Structure Quasiparticle and Optical Gapsmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Saritas

Krogel

Okamoto

et al. 2019

Phys. Rev. Materials

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“…1(b for the actual structure), whose total energy is estimated as E tot (chain) = −33.99 eV. Thus, the total energies of the two structures turn out to be quite close to each other; considering the accuracy of the first principles calculation, a difference of 40 meV can be reversed, e.g., by the effects of the correlation and/or excess oxygens not taken into account here [55]. Then, given the fact that the chain-type structure is known to be realized in an existing material Sr 2 CuO 3 [18][19][20] but inconsistent with the tetragonal symmetry, the Lieb-latticetype structure may be considered as a realistic candidate for the lattice structure of Ba 2 CuO 3+δ .…”

Section: A Stability Of the Lieb Structure For Ba 2 Cuomentioning

confidence: 82%

Superconducting mechanism for the cuprate Ba2CuO3+δ based on a multiorbital Lieb lattice model

Yamazaki

Ochi

Ogura

et al. 2020

Phys. Rev. Research

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For the recently discovered cuprate superconductor Ba 2 CuO 3+δ , we propose a lattice structure which resembles the model considered by Lieb to represent the vastly oxygen-deficient material. We first investigate the stability of the Lieb-lattice structure and then construct a multiorbital Hubbard model based on first-principles calculation. By applying the fluctuation-exchange approximation to the model and solving the linearized Eliashberg equation, we show that s-wave and d-wave pairings closely compete with each other and, more interestingly, that the intraorbital and interorbital pairings coexist. We further show that if the energy of the d 3z 2 −r 2 band is raised to make it "incipient" with the lower edge of the band close to the Fermi level within a realistic band filling regime, s±-wave superconductivity is strongly enhanced. We reveal an intriguing relation between the Lieb model and the two-orbital model for the usual K 2 NiF 4 structure where a close competition between sand d-wave pairings is known to occur. The enhanced superconductivity in the present model is further shown to be related to an enhancement found previously in the bilayer Hubbard model with an incipient band.

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“…For Mn and O atoms, we used hard norm-conserving RRKJ (OPT) pseudopotentials 50 . These potentials have been thoroughly tested in previous DMC works for Mn and O-based materials 33,50 . For these pseudopotentials, we used a kinetic energy cutoff of 300 Ry.…”

Section: Methodsmentioning

confidence: 99%

“…This method has a weaker dependence on the starting Hubbard parameter and density functional and can successfully achieve results with an accuracy beyond the mean field approximation 19 . For example, DMC has succesfully been used to calculate the spin superexchange in the correlated cuprate Ca 2 CuO 3 31 , has been used to successfully predict the magnetic structure in FeSe when DFT methods disagreed 32 , and has been applied to bulk polymorphs of MnO 2 to achieve band gap and lattice constant values in excellent agreement with experiment 33 and has been applied to study the excitation energies of Mn 4+ doped phosphors 41 (both Mn-based studies used the same RRKJ pseudopotentials we used in our work 33,41 ).…”

Section: Introductionmentioning

confidence: 99%

The intrinsic ferromagnetism of two-dimensional (2D) MnO$_2$ revisited: A many-body Quantum Monte Carlo and DFT+U study

Wines,

Saritas,

Ataca

2021

Preprint

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is one of the few predicted two-dimensional (2D) ferromagnets that has been experimentally synthesized and is commercially available. It is known that the Ising-like spin Hamiltonian is not valid for 2D systems, as a consequence of the Mermin-Wagner theorem, which states that magnetic order in a 2D material cannot persist unless magnetic anisotropy (MA) is present and perpendicular to the plane. Previous computational studies have predicted the magnetic ordering and Curie temperature of 2D MnO 2 with DFT+U (Density Funtional Theory + Hubbard U correction), with the results having a strong dependence on the Hubbard U parameter. Diffusion Monte Carlo (DMC) is a correlated electronic structure method that has had demonstrated success for the electronic and magnetic properties of a variety of 2D and bulk systems since it has a weaker dependence on the starting Hubbard parameter and density functional. In this study, we used DMC and DFT+U to calculate the magnetic properties of monolayer MnO 2 . We found that the ferromagnetic ordering is more favorable than antiferromagnetic and determined a statistical bound on the magnetic exchange parameter (J). In addition, we performed spin-orbit MA energy calculations using DFT+U and using our DMC and DFT+U parameters along with the analytical model of Torelli and Olsen 1 , we estimated an upper bound of 28.8 K for the critical temperature of MnO 2 . These QMC results intend to serve as an accurate theoretical benchmark, necessary for the realization and development of future 2D magnetic devices. These results also demonstrate the need for accurate methodologies to predict magnetic properties of correlated 2D materials.

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Diffusion Monte Carlo: A pathway towards an accurate theoretical description of manganese oxides

Cited by 18 publications

References 119 publications

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Structural, electronic, and magnetic properties of bulk and epitaxial LaCoO3 through diffusion Monte Carlo

Superconducting mechanism for the cuprate Ba2CuO3+δ based on a multiorbital Lieb lattice model

The intrinsic ferromagnetism of two-dimensional (2D) MnO$_2$ revisited: A many-body Quantum Monte Carlo and DFT+U study

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