A DFT+DMFT Investigation on Electron-Phonon Coupling in FeSe*

The dramatic increase of superconducting temperature with external pressure in undoped FeSe has opened up a new route to investigate the mechanism of superconductivity. Using the self-consistent density functional theory-dynamical mean field theory (DFT-DMFT) method for paramagnetic FeSe as a function of compression, we find that there is greatly enhanced coupling between some correlated electron states between $\Gamma$ and Z points and the $A_{1g}$ lattice distortion. Except at high pressure, the maximum deformation potential in DFT for this mode is insensitive to increasing pressure, whereas the corresponding DFT-DMFT maximum deformation potential shows the same behavior with pressure as the experimental $T_c$, which first increases and then decreases with pressure. The Fermi surface average of the deformation potential in DFT-DMFT method can increase up to 50\% when compared to standard DFT