  Electronic states of single-component molecular metals M(tmdt)2 (M = Ni, Au)
are studied theoretically. We construct an effective three-band Hubbard model
for each material by numerical fitting to first-principles band calculations,
while referring to molecular orbital calculations for the isolated molecules.
The model consists of two kinds of base orbital for each molecule with
hybridization between them, i.e., a \pi-character orbital for each of the two
tmdt ligands, and, a pd\pi-orbital for M = Ni or a pd\sigma-orbital for M = Au
centered on the metal site; this indicates that these materials can be
considered as novel multiband \pi-d systems. We find that both orbitals
contribute to realize the metallic character in Ni(tmdt)2. The origin of the
antiferromagnetic transition observed in Au(tmdt)2 is also discussed based on
this model.
