Ab initio electronic structure calculation for single-component molecular conductor Au(tmdt)2 (tmdt = trimethylenetetrathiafulvalenedithiolate)

We have investigated the electronic structure of Au(tmdt)(2) (tmdt = trimethylenetetrathiafulvalenedithiolate), which is a single-component conductor showing a magnetic phase transition around 100K, by ab initio plane-wave pseudopotential calculations. A single band crosses the Fermi level. This band and the next band below are a result of the strong hybridization between the two neighboring molecular levels near the Fermi level (SOMO and HOMO-1) and the system is more properly described as quarter-filled rather than half-filled in the strong correlation regime. The Fermi surface has corrugated-sheet-like parts nearly parallel to each other. Intraband generalized susceptibility suggests the presence of a nesting vector a*/2 (a* is one of the reciprocal lattice vectors). Spin-polarized calculation on the doubled unit cell along the a axis (a is a lattice vector) results in an antiferromagnetic order. The nesting is not perfect and Fermi-surface pockets remain in the magnetic phase. The implications of the present calculations with regard to experimental results are discussed.