Large-scale calculations of the E1 strength are performed within the random
phase approximation (RPA) based on the relativistic point-coupling mean field
approach in order to derive the radiative neutron capture cross sections for
all nuclei of astrophysical interest. While the coupling to the single-particle
continuum is taken into account in an explicit and self-consistent way,
additional corrections like the coupling to complex configurations and the
temperature and deformation effects are included in a phenomenological way to
account for a complete description of the nuclear dynamical problem. It is
shown that the resulting E1-strength function based on the PCF1 force is in
close agreement with photoabsorption data as well as the available experimental
E1 strength data at low energies. For neutron-rich nuclei, as well as light
neutron-deficient nuclei, a low-lying so-called pygmy resonance is found
systematically in the 5-10 MeV region. The corresponding strength can reach 10%
of the giant dipole strength in the neutron-rich region and about 5% in the
neutron-deficient region, and is found to be reduced in the vicinity of the
shell closures. Finally, the neutron capture reaction rates of neutron-rich
nuclei is found to be about 2-5 times larger than those predicted on the basis
of the nonrelativistic RPA calculation and about a factor 50 larger than
obtained with traditional Lorentzian-type approaches.Comment: 11 pages, 12 figure
