The interaction between the magnesium (Mg) atom and Alq3 molecule in organic light emitting devices has been theoretically studied using the PM3 method of the molecular orbital theory. It has been shown that various interactions can happen when the Mg atom approaches the Alq3 molecule, leading to significant changes in the molecular geometry and electronic structure of Alq3. The resulting configurations with insertion of Mg into the central part of the Alq3 molecule are found to be energetically more favorable than those with Mg forming bond(s) with a benzene ring of Alq3. In agreement with recent experiments, this result shows that the interaction between Mg and the Alq3 molecule depends on the order of deposition. Interestingly, the density of states calculated for these systems reveals that the creation of the new electronic gap states observed in the experiments is mainly relating to the aluminum atomic orbital due to interaction, instead of a direct contribution of Mg.

The interactions of benzene (C6H6), naphthalene (C10H8), and perinaphthene (C13H9) with metal atoms (Li, Ca, and Al) were studied using second-order Møller-Plesset perturbation theory. By analyzing the frontier molecular orbitals, geometric structures, binding energies, and charge transfers, it was found that these metal atoms can bond strongly with C13H9, but can only bond weakly with C6H6 and C10H8. The bonding nature between a metal atom and C13H9 at their ground state depends significantly on the valence orbital of the metal atom and the pi-bonding distribution of the aromatic hydrocarbons. The spindly shaped 3p valence orbital of an Al atom results in the deviation of the adsorption site to the edge of C13H9, whereas the ball-shaped 2s/4s valence orbitals of a Li and a Ca atom facilitate their overlap with the second lowest unoccupied molecular orbital of C13H9. Further, Hartree-Fock and density-functional theory methods were demonstrated generally to be unreliable in describing the interactions of metal atoms with these pi systems.