DFT+DMFT Study of the lattice disorder effect due to molecular conformations in a band-width controlled Mott insulating organic material

κ-(BEDT-TTF)₂X organic is a well-known typical Mott insulator in which the metal-insulator transition is driven by the narrow electronic band-width between molecular orbitals. Here, we study the lattice disorder effect from subtle molecular conformations due to the rotation of molecular orbitals on electronic structure of this strongly organic material using density functional plus dynamical mean field theory. Near the metal-insulator transition boundary, the organic structure with the homogeneous eclipsed conformation exhibits a Fermi-liquid metallic state while the same-volume structure with the homogeneous staggered conformation becomes a Mott insulator. Remarkably, the inhomogeneous configuration of both eclipsed and staggered conformations can also induce the Mott insulating state since the electronic band-width is much reduced than that of the homogeneous eclipsed one while the energy of the inhomogeneous phase is lower than that of the Mott insulating staggered structure. Our results show that the lattice disorder effect due to inhomogeneous molecular conformations can play an important role to the study of the Mott transition in this and related correlated organic materials.