On the dissociation energy of Ti(OH₂)⁺. An MCSCF, CCSD(T), and DFT study

The dissociation energy of the Ti(OH 2 ) + ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations d n−1 s and d n−2 s 2 of the 4 F electronic state of the titanium cation were also calculated and are discussed.