Density functional theory combined with the restricted open-shell Hartree-Fock method using the B3LYP, BLYP, and B3PW91 exchange-correlation functionals in the 6-311G** basis has been applied to determine equilibrium geometry of water-containing clusters 1 (H 3 O + -nH 2 O) with n = 1-3, 5, 6 and 1 (H 3 O + -3H 2 O)Cl -. The SA-MCSCF simulation has revealed a series of electronic terms of hydroxonium ion and energy profiles of its formation. Energy profiles of H 3 O + interaction with H 2 O have been simulated and analyzed. Vibrational spectra have been simulated for all the mentioned complexes in the equilibrium state, and regularities of changes of the fundamental vibrational frequencies with the increasing nuclearity of the complexes have been discovered.