Using an embedding approach, a 2D potential energy function has been calculated to describe the physisorption interaction of H2 with a Cu(100) surface. For this purpose, a cluster model of the system calculated with highly correlated wavefunctions is combined with a periodic DFT method using vdW-DF2 functional. Rotational and vibrational energy levels of physisorbed H2, as well as D2 and HD, are calculated using the 2D embedding corrected potential energy function. The calculated transitions are in a very good agreement with EELS observations. This contribution proposes a combined approach: cluster, periodic, embedded, to describe the physisorption potential of H2 on a metallic surface. The accuracy of the shape of the potential is checked by a spectroscopic analysis which agrees with experiment.