Expressions are obtained for calculation of the direct and exchange matrix elements of the energy operator for the orbit-orbit and electrostatic interactions in the representation of uncoupled angular momenta for the pf configuration. Comparison of the expressions for exchange matrix elements of these interactions showed their similarity. This allows one to additionally verify the matrix elements of the orbit-orbit interaction, whose calculation is more complicated, compared to that of the electrostatic matrix elements. The angular parts of the matrix elements are calculated using the formalism of irreducible tensor operators. The correctness of the expressions derived for the pf electron configuration was also verified in the LSJM representation. The orbit-orbit interaction is represented in the matrix elements by the radial integrals of the Marvin spin interactions.