Both first principles pseudopotential calculations and atomistic simulations have been employed to study the MgO{100}/Ag{100} and MgO{110}/Ag{110} interfaces. For both interfaces the most stable structure was determined to be where the Ag atoms are situated above the O2- ion. The binding energy for the {110} interface is approximately three times greater than for the {100} interface. The relative binding energies for the two interfaces is reflected in the Ag to O2- distance and the electron distortion on the Ag atom. The binding energies have been determined with the local density approximation and generalized gradient approximation GGA to the exchange-correlation energy. The binding energies calculated using an atomistic simulation model are similar to the GGA results. However, the calculation of short-range potentials using the electron gas method is an oversimplification.