Each monomer "borrows" functions from other nearby components, effectively increasing its basis set and improving the calculation of derived properties such as energy.
Other than using infinite basis sets, two methods exist to eliminate the BSSE.
In the chemical Hamiltonian approach (CHA),[4][5] basis set mixing is prevented a priori, by replacing the conventional Hamiltonian with one in which all the projector-containing terms that would allow mixing have been removed.
[2] It however has been shown that there is an inherent danger in using counterpoise corrected energy surfaces, due to the inconsistent effect of the correction in different areas of the energy surface.
Whereas in the CHA model, those orbitals have no greater intrinsic freedom and therefore the correction treats all fragments equally.