Computer simulations based on the first principles calculations play a central role in helping us understand, predict, and engineer physical, chemical, and electronic properties of technologically relevant materials. While density functional theory (DFT) or DFT+U methods give quite accurate results for structural parameters in most materials, qualitative predictions of excitedstate properties usually require beyond DFT methods, such as the metaGGA, hybrid functionals, GW approximation, or the dynamical meanfield theory (DMFT). Here I highlight my work in two popular approaches that go beyond the standard DFT. First, with the DMFT in combination with DFT, I will present the anomalous properties of the ironbased superconductors in both bulk and monolayer phases. In particular, I will discuss how electron correlation affects the strength of electronphonon coupling in FeSe, which has been recently investigated in a femtosecond coherent lockedin photoemission spectroscopy experiment [2,3]. Another abinitio beyondDFT method is GWapproximation, which is extensively used to compute excited states of electrons in solids. So far, most of the GW calculations have been confined to small unitcell of bulklike materials due to the extreme computational demand of the approach. I will discuss my collaborative effort toward developing a highly scalable and opensource GW software, OpenAtom, to compute electronic excited states more efficiently for petascale architectures using the Charm++ parallel framework [4,5].
Now that various beyondDFT methods are available, it is very often unclear how accurate these methods can be expected to be when applied to a given strongly correlated solid. Thus, it is a pressing interest to compare their accuracy as they apply to different categories of materials, and at the same time, to build up a database of correlated materials using various beyondDFT methods. I will conclude with a brief discussion in this direction and discuss our recent progress in comparative study of these methods on a few training sets of correlated materials [6].
References:
S. Mandal, P. Zhang, S. IsmailBeigi, K. Haule; “How correlated is the FeSe/SrTiO3 system?”,
Phys. Rev. Lett. 119, 067004 (2017).

S. Mandal, R. E. Cohen, and K. Haule; “Strong Pressure Dependent ElectronPhonon Coupling in FeSe”,
Phys. Rev. B (R) 89, 220502(R) (2014).

S. Gerber et al.; “Femtosecond electronphonon lockin by photoemission and xray freeelectron laser”,
Science 357, 71 (2017).

M. Kim*. S. Mandal* et al. “Scalable GW software for quasiparticle properties using OpenAtom”,
Comp. Phys. Comm., 244, 427 (2019).

http://charm.cs.illinois.edu/OpenAtom/

S. Mandal, K. Haule, K. M. Rabe, and D. Vanderbilt: “Systematic beyondDFT study of binary transition metal oxides” npj. Comput. Mater. 5, 115 (2019).