The collective Hamiltonian including isovector pairing and [Formula: see text]-particle-type correlation degrees of freedom is constructed. The Hamiltonian is applied to description of the relative energies of the ground states of even–even nuclei around [Formula: see text]Ni. A satisfactory description of the experimental data is obtained. A significant improvement of the agreement with the experimental data compared to our previous calculations is explained by inclusion in the Hamiltonian of the dynamical variables describing [Formula: see text]-particle-type correlations.