Considerable complexity is introduced by short range correlationsdue to the strong bare interactions between nucleons, to shell model wave functions. Still, in a variety of nuclear phenomena, it seems as if single nucleon wave functions, as assumed in the shell model, have definite reality. Single nucleon wave functions are also used to calculate successfully certain observables. A certain procedure of obtaining these functions is to adopt a potential well whose radius is determined by the measured charge distribution of the nucleus considered. Its depth is usually adjusted to make the single nucleon energy equal to the difference between the binding energy of the nucleus considered and the binding energy of the nucleus from which the nucleon is removed (separation energy). This prescription will be examined and a more adequate one will be suggested.
