Stability of correlated insulating states in molecular conductors from first-principles calculation

Electronic properties of molecular conductors exhibiting antiferromagnetic (AFM) spin order and charge order (CO) owing to electron correlation are studied using first-principles density functional theory calculations. We investigate two systems, a quasi-two-dimensional Mott insulator β^-(BEDT-TTF)₂ICl₂ with an AFM ground state, and several members of quasi-one-dimensional (TMTTF)₂X$ showing CO. The stabilities of the AFM and CO states are compared between the use of a standard exchange-correlation functional based on the generalized gradient approximation and that of a range-separated hybrid functional; we find that the latter describes these states better. For β^-(BEDT-TTF)₂ICl₂, the AFM order is much stabilized with a wider band gap. For (TMTTF)₂X$, only by using the hybrid functional, the AFM insulating state is realized and the CO states coexisting with AFM order are stable under structural optimization, whose stability among different X shows the tendency consistent with experiments.