The link between Hundsness and superconductivity
The numerically exact solutions of the uniform electron gas problem by variational diagrammatic Monte Carlo method at metallic densities [1,2] gave us new insights into the screening in solids and show that in metallic solids the short-range interaction point of view is most appropriate for fast convergence towards the exact solution. This gives us a new understanding of why embedding through Dynamical Mean Field Theory (DMFT) has been so successful in describing numerous correlated solids. In this talk, I will highlight a few examples of DFT+embedded DMFT functional predictions verified experimentally, including prediction of electron-phonon coupling in FeSe[3,4], strong incoherence of the normal state in Fe superconductors and its Hund's coupling origin. I will show that the Hundsness in these superconductors has huge effect on both the normal and the superconducting state properties [3-6] as well as the lattice dynamics and electron-phonon coupling.
 A combined variational and diagrammatic quantum Monte Carlo approach to the many-electron problem, Kun Chen and Kristjan Haule, Nature Communications, 10(1):3725, 2019.
 Single-particle excitations in the uniform electron gas by diagrammatic Monte Carlo, Kristjan Haule and Kun Chen, Scientific Reports, 12(1):2294, 2022.
 Strong pressure-dependent electron-phonon coupling in FeSe, Subhasish Mandal, R. E. Cohen, and K. Haule, Phys. Rev. B 89, 220502(R) (2014).
 Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser, Gerber S, Z.X.Shen, et.al., Science 357, 6346 (July 2017).
 Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors, Z. P. Yin, K. Haule, and G. Kotliar, Nature Physics 10, 845–850 (2014).
 Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides, Z. P. Yin, K. Haule, G. Kotliar, Nature Materials 10, 932-935 (2011).