How reliable is the Lippincott-Schroeder potential for the OH…N hydrogen bonded fragment in the gas phase?

Ab initio calculations at the MP2 level of theory, with a 6–31 G basis set which includes polarization functions on the atoms involved in the H bond, are performed on the hydrogen-bonded phenol-NH3 complex. The equilibrium O…N distance (Re) is equal to 2.837 Å. The potential profile along the proton coordinate at a fixed O…N distance V(r, Re) only one minimum. Its shape is verified by calculation of the OH stretch frequency. The Lippincott-Schroeder potential is able to reproduce the shape of the V(r, Re) function for systems with an OH…N fragment in the gas phase only if some its parameters are calibrated to fit high-level ab initio data.