in Figs. \[fig3\](b) and (c); in the unit cell, the two L sites from different molecules form L1-L2 dimers. The degree of dimerization, represented by the intradimer transfer integral, namely, that along the L1-L2 B bond, is largest in \[Cu(tmdt)$_2$\]. This dimerized structure resembles the situation commonly seen in typical CTS, e.g., in TM$_2X$ and polytypes of ET$_2X$ such as the $\kappa$ and $\beta$-types [@Review_2006JPSJ; @Seo_2004CR]. M$\pi$ orbitals, in contrast, do not have large $t_{lm}$ between them, but bridge L layers mainly along the intramolecular bonds. They are appreciable (0.1 - 0.2 eV) and then these two orbitals mix with each other. The main differences between the three compounds are in orbital energy, which we will discuss in the next subsection.

![(Color online) \[$M$(tmdt)$_2$\] viewed along the molecular long axis (a) and schematic views of fMO model with lattice sites represented as circles \[(b) and (c)\]. The unit cell containing one molecule with four orbitals is shown as gray lines, and notations for intermolecular bonds are indicated whose correspondences are A \[100\], B \[111\], C \[101\], P \[211\], Q \[001\], and R \[011\]. The two-dimensional network of L sites is shown in (b), perpendicular to the plane, and in (c); 