  The strength functions of the DGDRs in 16O and 40Ca are calculated using an
extended version of TDHF known as the time-dependent density-matrix theory
(TDDM). The calculations are done in a self-consistent manner, in which the
same Skyrme force as that used for the mean-field potential is used as the
residual interaction to calculate two-body correlations. It is found that the
DGDR in 16O has a large width due to the Landau damping, although the centroid
energy of the DGDR is close to twice the energy of the GDR calculated in RPA.
The DGDR in 40Ca is found more harmonic than that in 16O.
