  The adiabatic potential energy curves of Rb$_2$ in the long-range Rydberg
electronic states are calculated using the two-electron \textit{R}-matrix
method [M. Tarana, R. \v{C}ur\'{i}k, Phys. Rev. A \textbf{93}, 012515 (2016)]
for the intermediate internuclear separations between 35 a.u. and 200 a.u. The
results are compared with the zero-range models to find a region of the
internuclear distances where the Fermi's pseudopotential approach provides
accurate energies. A finite-range potential model of the atomic perturber is
used to calculate the wave functions of the Rydberg electron and their features
specific for the studied range of internuclear distances are identified.
