Prediction of the electron redundant SinNn fullerenes

Highlights: • One Si atom in each Si₂N₂ square protrudes obviously and the cages of Si_mAl_n-mN_n and Si_nN_n deform. • The electron redundant Si_mAl_n-mN_n and Si_nN_n cages are more stable than the corresponding stoichiometric Al_nN_n. • The excess electrons in Si_mAl_n-mN_n and Si_nN_n reside at outside of the protrudent Si atoms as lone pair electrons. • The orbital interactions between Si and N atoms are stronger than that between Al and N atoms. The stabilities and electronic structures of Si_mAl_n-mN_n and Si_nN_n (n = 16, 20, m = 12 and n = 24, m = 16) fullerene-like cages have been investigated using density functional method B3LYP and the second-order perturbation theory MP2. The results show that the Si_mAl_n-mN_n and Si_nN_n fullerenes are more stable than the AlN counterparts. Comparing with the corresponding Al_nN_n cages, one silicon atom in each Si₂N₂ square protrudes and the excess electrons reside as lone pair electrons at the outside of the protrudent Si atoms. Analyses on the electronic structures suggest that the SiN bonds are covalent bonding with strong polarity. The ELF (electron localization function) shows large electron pair probability between Si and N atoms. The orbital interactions between Si and N are stronger than that between Al and N atoms; the overlap integral is 0.40 per SiN bond in Si_nN_n and 0.34 per AlN bond in Al_nN_n. The AIM (atoms in molecule) charges on the Al atoms in Al_nN_n and Si_mAl_n-mN_n are 2.37 and 2.40. The charges on the in-plane and protrudent Si atoms are about 2.88 and 1.50 respectively. Considering the large local dipole moments around the protrudent Si atoms, the electrostatic interactions are also favorable to the SiN cages.