  The importance of taking into account inter-site $f-f$ hybridization in
electron structure calculations for Ce metal and cerium heavy fermion compounds
was studied. We demonstrate that for heavy-fermion systems such as cerium
compound CeCu$_2$Si$_2$ $f-f$ hybridization can be neglected and Anderson model
application is well justified. On another hand for cerium metal $f-f$
hybridization is strong enough to provide the contribution to hybridization
function comparable to hybridization between $4f$ and itinerant electrons. We
argue that in the case of Ce only the most general Hamiltonian combining
Hubbard and Anderson models should be used.
