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Register a new userFree energy from stationary implementation of the DFT+DMFT functional
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The stationary functional of the all-electron density functional plus dynamical mean field theory (DFT+DMFT) formalism to perform free energy calculations and structural relaxations is implemented for the first time. Here, the first order error in the density leads to a much smaller, second order error in the free energy. The method is applied to several well known correlated materials; metallic SrVO$_3$, Mott insulating FeO, and elemental Cerium, to show that it predicts the lattice constants with very high accuracy. In Cerium, we show that our method predicts the iso-structural transition between the $alpha$ and $gamma$ phases, and resolve the long standing controversy in the driving mechanism of this transition.
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We implemented the derivative of the free energy functional with respect to the atom displacements, so called force, within the combination of Density Functional Theory and the Embedded Dynamical Mean Field Theory. We show that in combination with the numerically exact quantum Monte Carlo (MC) impurity solver, the MC noise cancels to a great extend, so that the method can be used very efficiently for structural optimization of correlated electron materials. As an application of the method, we show how strengthening of the fluctuating moment in FeSe superconductor leads to a substantial increase of the anion height, and consequently to a very large effective mass, and also strong orbital differentiation.
We have investigated the temperature (T)-dependent evolution of electronic structures and magnetic properties of an itinerant ferromagnet SrRuO3, employing the combined scheme of the density functional theory and the dynamical mean-field theory (DFT+DMFT). The inclusion of finite dynamical correlation effects beyond the DFT well describes not only the incoherent hump structure observed in the photoemission experiment but also the T-dependent magnetic properties in accordance with experiments. We have shown that the magnetization of SrRuO3 evolves with the Stoner behavior below the Curie temperature (Tc), reflecting the weak itinerant ferromagnetic behavior, but the local residual magnetic moment persists even above Tc, indicating the local magnetic moment behavior. We suggest that the ferromagnetism of SrRuO3 has dual nature of both weak and local moment limits, even though the magnetism of SrRuO3 is more itinerant than that of Fe.
The sensitivity of Density Functional Theory plus Dynamical Mean Field Theory calculations to different constructions of the correlated orbitals is investigated via a detailed comparison of results obtained for the quantum material NdNiO$_2$ using different Wannier and projector methods to define the correlation problem. Using the same interaction parameters we find that the different methods produce different results for the orbital and band basis mass enhancements and for the orbital occupancies, with differing implications regarding the importance of multiorbital effects and charge transfer physics. Using interaction parameters derived from cRPA enhances the difference in results. For the isostructural cuprate CaCuO$_2$, the different methods give quantitatively different mass enhancements but still result in the same qualitative physics.
We present a theoretical investigation of the electronic structure of rutile (metallic) and M$_1$ and M$_2$ monoclinic (insulating) phases of VO$_2$ employing a fully self-consistent combination of density functional theory and embedded dynamical mean field theory calculations. We describe the electronic structure of the metallic and both insulating phases of VO$_2$, and propose a distinct mechanism for the gap opening. We show that Mott physics plays an essential role in all phases of VO$_2$: undimerized vanadium atoms undergo classical Mott transition through local moment formation (in the M$_2$ phase), while strong superexchange within V-dimers adds significant dynamic intersite correlations, which remove the singularity of self-energy for dimerized V-atoms. The resulting transition from rutile to dimerized M$_1$ phase is adiabatically connected to Peierls-like transition, but is better characterized as the Mott transition in the presence of strong intersite exchange. As a consequence of Mott physics, the gap in the dimerized M$_1$ phase is temperature dependent. The sole increase of electronic temperature collapses the gap, reminiscent of recent experiments.
We study the dopant-induced inhomogeneity effect on the electronic properties of heavy fermionCeCoIn5using a combined approach of density functional theory (DFT) and dynamical mean-field theory (DMFT). The inhomogeneity of the hybridization between Ce-4fand conduction electrons is introduced to impose the inequivalent Ce atoms with respect to the dopant. From the DFT to the DFT+DMFT results, we demonstrate a variation of the hybridization strength depending on the hole or electron doping. A drastic asymmetric mass renormalization could be reproduced in the DFT+DMFT calculation. Finally, the calculated coherence temperature reflects the different development of the heavy quasiparticle states, depending on the dopant.
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