First-principles study of the electronic structure of the organic solids ${(\mathrm{C}\mathrm{H}}_3{)}_4\mathrm{N}\left[M\right(\mathrm{dmit}{)}_2{]}_2$ ($M=\mathrm{Ni}$ and Pd): Role of dimerization and the stability of the formation of a dimer

The electronic structures of organic solids ${(\mathrm{C}\mathrm{H}}_3{)}_4{\mathrm{N}\left[\mathrm{Ni}\right(\mathrm{dmit})\mathrm{}}_2{]}_2$ and $\beta -{(\mathrm{C}\mathrm{H}}_3{)}_4{\mathrm{N}\left[\mathrm{Pd}\right(\mathrm{dmit})\mathrm{}}_2{]}_2$ (dmit=2-thioxo-1,3-dithion-4,5-dithiolate) are studied by first-principles calculations based on the density functional theory. We have found that the electronic structure of the Ni salt shows strong one-dimensional character, while that of the Pd salt shows two-dimensional character. These results agree with experimental results. We show that the differences mainly come from the degree of dimerization. By calculating the stable structure of the isolated dimer, we have found that the difference of the degree of dimerization is due to the different character of $M(\mathrm{dmit}{)}_2$ itself.