Induced dipole moment of physisorbed rare gas atoms

We discuss models used for numerical estimations of induced dipoles in physisorption. In the case of perfect mirror the harmonic oscillator and Unsöld models are compared to the exact calculation done by using a coefficient introduced by Byers-Brown and Whisnant; which leads us to give, for the first time, an accurate value of the induced dipole for hydrogen and rare gas atoms. Even for more realistic surfaces the oscillator and the Unsöld models underestimate the dipole moment.