For two identical atoms, how to use an all electron basis set for one atom and a pseudopotential(ECP) for the other atom

For example, in the calculation of an oxygen molecule, one O atom can be described using the def2-VTZP basis set, while the other O atom can be described using the Stuttgart RLC ECP basis set. How should the basis set section in the input file be written?

This capability does not exist. It would essentially be the ‘BASIS = MIXED’ equivalent of ECP = …, but no such feature is implemented, as previously discussed here: