The problem of the partial inclusion of electron correlation effects has been considered in the framework of the unrestricted Hartree-Fock method. The calculation of the electronic structure of the [Ti₂O₉]^12- cluster is performed. The results obtained demonstrate that, in some cases, a major part of static correlation effects can be taken into account in the unrestricted Hartree-Fock approximation. The influence of these effects on the local characteristics of crystals is analyzed.