Ab initio versus CNDO potential surface calculations for Li2O and Al2O

Potential surfaces for Li₂O and Al₂O have been calculated by an ab initio SCF-LCAO-MO method and by the semiempirical CNDO method. For both molecules the semiempirical methods incorrectly imply unreasonable structures with very acute apex angles and very long bond distances — rather more like diatomic Li₂ or Al₂ molecules with O-atoms attached to their bonds. Our ab initio treatment does correctly predict a symmetrical linear configuration for Li₂O with bond distances in excellent agreement with experiment. This method also predicts a linear symmetrical structure for Al₂O, in agreement with experimental gas phase measurements but in disagreement with matrix-isolation studies.