Effective models for the low energy behavior of FeSe from first principles quantum Monte Carlo

A major question in the study of iron-based superconductors is what appropriate effective model applies to them. Recently[1], it has become possible to use highly accurate fixed-node diffusion Monte Carlo (FN-DMC) calculations to derive effective models for correlated electron systems. Previous work[2] by our group has shown that FN-DMC provides an accurate accounting of several properties of FeSe. We combine FN-DMC calculations with the model-fitting approach in [1] and a matching pursuit approach to quantify the importance of different interaction and hopping parameters to algorithmically select multiple minimal models for the low-energy degrees of freedom of the system using only first principles data. We will discuss these models and what they mean for the description of this system. [1] H. J. Changlani, H. Zheng, and L. K. Wagner, The Journal of Chemical Physics 143, 102814 (2015). [2] B. Busemeyer, M. Dagrada, S. Sorella, M. Casula, L. K. Wagner, Physical Review B 94, 035108 (2016).