  We present a method for calculation of the second-order exchange-dispersion
energy in the framework of the symmetry-adapted perturbation theory (SAPT) for
weakly interacting monomers described with multiconfigurational wave functions.
The proposed formalism is based on response properties obtained from extended
random phase approximation (ERPA) equations and assumes the single-exchange
(S2) approximation. The approach is applicable to closed shell systems where
static correlation cannot be neglected or to systems in nondegenerate excited
states. We examine the new method in combination with either generalized
valence bond perfect pairing (GVB) or complete active space self consistent
field (CASSCF) description of the interacting monomers. For model
multireference dimers in ground-states (H2-H2, Be-Be, He-H2)
exchange-dispersion energies are reproduced accurately. For the interaction
between the excited hydrogen molecule and the helium atom we found unacceptably
large errors which is attributed to the neglect of diagonal double excitations
in the employed approximation to the linear response function.
