  Background: The quasiparticle random phase approximation (QRPA), within the
framework of the nuclear density functional theory (DFT), has been a standard
tool to access the collective excitations of the atomic nuclei. Recently,
finite amplitude method (FAM) has been developed, in order to perform the QRPA
calculations efficiently without any truncation on the two-quasiparticle model
space. Purpose: We discuss the nuclear giant dipole resonance (GDR) in heavy
rare-earth isotopes, for which the conventional matrix diagonalization of the
QRPA is numerically demanding. A role of the Thomas-Reiche-Kuhn (TRK) sum rule
enhancement factor, connected to the isovector effective mass, is also
investigated. Methods: The electric dipole photoabsorption cross section was
calculated within a parallelized FAM-QRPA scheme. We employed the Skyrme energy
density functional self-consistently in the DFT calculation for the ground
states and FAM-QRPA calculation for the excitations. Results: The mean GDR
frequency and width are mostly reproduced with the FAM-QRPA, when compared to
experimental data, although some deficiency is observed with isotopes heavier
than erbium. A role of the TRK enhancement factor in actual GDR strength is
clearly shown: its increment leads to a shift of the GDR strength to
higher-energy region, without a significant change in the transition
amplitudes. Conclusions: The newly developed FAM-QRPA scheme shows a remarkable
efficiency, which enables to perform systematic analysis of GDR for heavy
rare-earth nuclei. Theoretical deficiency of photoabsorption cross section
could not be improved by only adjusting the TRK enhancement factor, suggesting
the necessity of beyond the self-consistent QRPA approach, and/or a more
systematic optimization of the EDF parameters.
