molecules, from which the energy bands in their crystals near the Fermi energy are formed [@Ishibashi_2005JPSJ; @Ishibashi_2008JPSJ; @Ishibashi_2012Crystals]. Nonmagnetic wave functions and energy eigenvalues together with the electron occupation for isolated molecules are shown. The rough spatial extensions of the M$\sigma$, L, and M$\pi$ orbitals explained in the text are indicated. []{data-label="fig1"}](fig1.eps){width="8.4truecm"}

Molecular orbitals and fragment model {#subsec2-1}
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The band structures of isostructural SCMC near $\epsilon_{\rm F}$ are composed of several MO with similar characters upon chemical modifications [@Kobayashi_2004CR; @Ishibashi_2005JPSJ; @Ishibashi_2008JPSJ]; this applies to the family of \[$M$(tmdt)$_2$\] including the new member $M$ = Cu [@Zhou_2010IC; @Ishibashi_2012Crystals]. Four MO which mostly contribute to the electronic bands near $\epsilon_{\rm F}$ are shown in Fig. \[fig1\].

They can be approximately reconstructed using three kinds of fMO, which we call here M$\sigma$, L, and M$\pi$. The M$\sigma$ and M$\pi$ orbitals are the $p$-$d$ mixed wave functions, roughly being an anti-bonding combination of the metal site $d_{xy}$ and $d_{xz}$ orbitals, and the surrounding S $2p$ orbitals, respectively [@noteMnotation]. The relevant atomic $d$ orbitals are 3$d$ for $M$ = Ni and Cu, and 5$d$ for $M$ = Au. The L orbital is the $p\pi$ orbital which is similar to the HOMO of the TTF 