(DI-DCNQI)(2)CU 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 o f organic solids (DMe-DCNQI)(2)Cu and (DI-DCNQI)(2)Cu by first-princip les calculations based on density-functional theory. We have found tha t the electronic structure of (DI-DCNQI)(2)Cu changes drastically by a pplying pressure while that of (DMe-DCNQI)(2)Cu is almost unchanged. T he present calculation strongly suggests that the insulating phase of (DI-DCNQI)(2)Cu under pressure (similar or equal to-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 s tudied.