(DI-DCNQI)₂Cu as a unique member of the DCNQI-Cu family: A theoretical study of high-pressure phases

We have studied the pressure dependence of the electronic structures of organic solids (DMe-DCNQI)₂Cu and (DI-DCNQI)₂Cu by first-principles calculations based on density-functional theory. We have found that the electronic structure of (DI-DCNQI)₂Cu changes drastically by applying pressure while that of (DMe-DCNQI)₂Cu is almost unchanged. The present calculation strongly suggests that the insulating phase of (DI-DCNQI)₂Cu under pressure (≃16 kbar) will not have threefold periodicity along the c axis in clear contrast to other Cu salts. The metallic phase under high pressure (>35 kbar) is also studied.