Theoretical prediction of the structures and properties of cyclic AlS_2 and GaS_2 systems at density functional theory and all-electron correlation levels

摘要

The geometries and bonding properties have been predicted for cyclic AlS_2 and GaS_2 species at DFT,MPn(n=2,3,4), QCISD(T) and CCSD(T) levels with the 6-311+G~* basis set. Harmonic vibrational frequencies were determined using DFT and MP2 methods. The relevant energies were calibrated at high-order electron correlation levels. Each species possesses a ~2A_2 ground state with a higher-energy ~2A_1 state, lying 7.2 kcal/mol for AlS_2 or 20.0 kcal/mol for GaS_2 above at CCSD(T)/6-311+G~* level, and the corresponding CCSD(T) dissociation energies are 64.0 (AlS_2: ~2A_2) and 59.0 kcal/mol(GaS_2:~2A_2), respectively. Analysis indicates that the cyclic AlS_2 and GaS_2 should be classified as supersulfide, but they are not as ionic as NaO_2 and less ionic than AlO_2.